diff --git a/pkg/compiler/test/inference/data/call_site.dart b/pkg/compiler/test/inference/data/call_site.dart
index 6cc8406..16f18e0 100644
--- a/pkg/compiler/test/inference/data/call_site.dart
+++ b/pkg/compiler/test/inference/data/call_site.dart
@@ -112,7 +112,7 @@
 /*member: A8.:[exact=A8]*/
 class A8 {
   /*member: A8.x8:[empty]*/
-  x8(/*Union([exact=JSString], [subclass=JsLinkedHashMap])*/ p) =>
+  x8(/*Union([exact=JSString], [exact=JsLinkedHashMap])*/ p) =>
       /*invoke: [exact=A8]*/ x8("x");
 }
 
@@ -126,7 +126,7 @@
   /*member: A9.x9:[empty]*/ x9(
           /*[exact=JSUInt31]*/ p1,
           /*Union([exact=JSString], [exact=JSUInt31])*/ p2,
-          /*Union([exact=JSUInt31], [subclass=JsLinkedHashMap])*/ p3) =>
+          /*Union([exact=JSUInt31], [exact=JsLinkedHashMap])*/ p3) =>
       /*invoke: [exact=A9]*/ x9(p1, "x", {});
 }
 
diff --git a/pkg/compiler/test/inference/data/closure2.dart b/pkg/compiler/test/inference/data/closure2.dart
index 793c24c..a3c5e37 100644
--- a/pkg/compiler/test/inference/data/closure2.dart
+++ b/pkg/compiler/test/inference/data/closure2.dart
@@ -14,7 +14,7 @@
   return a;
 }
 
-/*member: returnDyn1:Union([exact=JSUInt31], [subclass=JsLinkedHashMap])*/
+/*member: returnDyn1:Union([exact=JSUInt31], [exact=JsLinkedHashMap])*/
 returnDyn1() {
   dynamic a = 42;
   // ignore: unused_local_variable
@@ -34,7 +34,7 @@
   return a;
 }
 
-/*member: returnDyn2:Union([exact=JSUInt31], [subclass=JsLinkedHashMap])*/
+/*member: returnDyn2:Union([exact=JSUInt31], [exact=JsLinkedHashMap])*/
 returnDyn2() {
   dynamic a = 42;
   // ignore: unused_local_variable
@@ -60,10 +60,10 @@
   return a;
 }
 
-/*member: returnDyn3:Union([exact=JSUInt31], [subclass=JsLinkedHashMap])*/
+/*member: returnDyn3:Union([exact=JSUInt31], [exact=JsLinkedHashMap])*/
 returnDyn3() {
   dynamic a = 42;
-  if (a /*invoke: Union([exact=JSUInt31], [subclass=JsLinkedHashMap])*/ == 53) {
+  if (a /*invoke: Union([exact=JSUInt31], [exact=JsLinkedHashMap])*/ == 53) {
     // ignore: unused_local_variable
     var f = /*[null]*/ () {
       a = {};
diff --git a/pkg/compiler/test/inference/data/closure_tracer.dart b/pkg/compiler/test/inference/data/closure_tracer.dart
index e689520..6353470 100644
--- a/pkg/compiler/test/inference/data/closure_tracer.dart
+++ b/pkg/compiler/test/inference/data/closure_tracer.dart
@@ -59,11 +59,11 @@
   dynamic b = <dynamic, dynamic>{'foo': 1};
 
   b
-      /*update: Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSUInt31]), map: {foo: [exact=JSUInt31], bar: Container([null|exact=JSExtendableArray], element: [subclass=Closure], length: 1)})*/
+      /*update: Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSUInt31]), map: {foo: [exact=JSUInt31], bar: Container([null|exact=JSExtendableArray], element: [subclass=Closure], length: 1)})*/
       ['bar'] = a;
 
   b
-          /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSUInt31]), map: {foo: [exact=JSUInt31], bar: Container([null|exact=JSExtendableArray], element: [subclass=Closure], length: 1)})*/
+          /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSUInt31]), map: {foo: [exact=JSUInt31], bar: Container([null|exact=JSExtendableArray], element: [subclass=Closure], length: 1)})*/
           ['bar']
 
       /*Container([null|exact=JSExtendableArray], element: [subclass=Closure], length: 1)*/
diff --git a/pkg/compiler/test/inference/data/dictionary_types.dart b/pkg/compiler/test/inference/data/dictionary_types.dart
index 61c0072..e8a191a 100644
--- a/pkg/compiler/test/inference/data/dictionary_types.dart
+++ b/pkg/compiler/test/inference/data/dictionary_types.dart
@@ -13,7 +13,7 @@
   test5();
 }
 
-/*member: dictionaryA1:Map([subclass=JsLinkedHashMap], key: [null|subclass=Object], value: [null|subclass=Object])*/
+/*member: dictionaryA1:Map([exact=JsLinkedHashMap], key: [null|subclass=Object], value: [null|subclass=Object])*/
 dynamic dictionaryA1 = {
   'string': "aString",
   'int': 42,
@@ -21,7 +21,7 @@
   'list': []
 };
 
-/*member: dictionaryB1:Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [null|subclass=Object], length: null), stringTwo: Value([null|exact=JSString], value: "anotherString"), intTwo: [null|exact=JSUInt31]})*/
+/*member: dictionaryB1:Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [null|subclass=Object], length: null), stringTwo: Value([null|exact=JSString], value: "anotherString"), intTwo: [null|exact=JSUInt31]})*/
 dynamic dictionaryB1 = {
   'string': "aString",
   'int': 42,
@@ -29,7 +29,7 @@
   'list': []
 };
 
-/*member: otherDict1:Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSString], [exact=JSUInt31]), map: {stringTwo: Value([exact=JSString], value: "anotherString"), intTwo: [exact=JSUInt31]})*/
+/*member: otherDict1:Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSString], [exact=JSUInt31]), map: {stringTwo: Value([exact=JSString], value: "anotherString"), intTwo: [exact=JSUInt31]})*/
 dynamic otherDict1 = {'stringTwo': "anotherString", 'intTwo': 84};
 
 /*member: int1:[exact=JSUInt31]*/
@@ -47,26 +47,26 @@
 /*member: test1:[null]*/
 test1() {
   dictionaryA1
-      . /*invoke: Map([subclass=JsLinkedHashMap], key: [null|subclass=Object], value: [null|subclass=Object])*/
+      . /*invoke: Map([exact=JsLinkedHashMap], key: [null|subclass=Object], value: [null|subclass=Object])*/
       addAll(otherDict1);
   dictionaryB1
-      . /*invoke: Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [null|subclass=Object], length: null), stringTwo: Value([null|exact=JSString], value: "anotherString"), intTwo: [null|exact=JSUInt31]})*/
+      . /*invoke: Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [null|subclass=Object], length: null), stringTwo: Value([null|exact=JSString], value: "anotherString"), intTwo: [null|exact=JSUInt31]})*/
       addAll({'stringTwo': "anotherString", 'intTwo': 84});
   int1 = dictionaryB1
-      /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [null|subclass=Object], length: null), stringTwo: Value([null|exact=JSString], value: "anotherString"), intTwo: [null|exact=JSUInt31]})*/
+      /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [null|subclass=Object], length: null), stringTwo: Value([null|exact=JSString], value: "anotherString"), intTwo: [null|exact=JSUInt31]})*/
       ['int'];
   anotherInt1 = otherDict1
-      /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSString], [exact=JSUInt31]), map: {stringTwo: Value([exact=JSString], value: "anotherString"), intTwo: [exact=JSUInt31]})*/
+      /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSString], [exact=JSUInt31]), map: {stringTwo: Value([exact=JSString], value: "anotherString"), intTwo: [exact=JSUInt31]})*/
       ['intTwo'];
   dynamic1 =
-      dictionaryA1 /*Map([subclass=JsLinkedHashMap], key: [null|subclass=Object], value: [null|subclass=Object])*/ [
+      dictionaryA1 /*Map([exact=JsLinkedHashMap], key: [null|subclass=Object], value: [null|subclass=Object])*/ [
           'int'];
   nullOrInt1 = dictionaryB1
-      /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [null|subclass=Object], length: null), stringTwo: Value([null|exact=JSString], value: "anotherString"), intTwo: [null|exact=JSUInt31]})*/
+      /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [null|subclass=Object], length: null), stringTwo: Value([null|exact=JSString], value: "anotherString"), intTwo: [null|exact=JSUInt31]})*/
       ['intTwo'];
 }
 
-/*member: dictionaryA2:Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
+/*member: dictionaryA2:Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
 dynamic dictionaryA2 = {
   'string': "aString",
   'int': 42,
@@ -74,7 +74,7 @@
   'list': []
 };
 
-/*member: dictionaryB2:Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), intTwo: [exact=JSUInt31], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
+/*member: dictionaryB2:Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), intTwo: [exact=JSUInt31], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
 dynamic dictionaryB2 = {'string': "aString", 'intTwo': 42, 'list': []};
 
 /*member: nullOrInt2:[null|exact=JSUInt31]*/
@@ -89,22 +89,22 @@
 /*member: test2:[null]*/
 test2() {
   var union = dictionaryA2
-          /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
+          /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
           ['foo']
       ? dictionaryA2
       : dictionaryB2;
   nullOrInt2 = union
-      /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {int: [null|exact=JSUInt31], double: [null|exact=JSNumNotInt], string: Value([exact=JSString], value: "aString"), intTwo: [null|exact=JSUInt31], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
+      /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {int: [null|exact=JSUInt31], double: [null|exact=JSNumNotInt], string: Value([exact=JSString], value: "aString"), intTwo: [null|exact=JSUInt31], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
       ['intTwo'];
   aString2 = union
-      /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {int: [null|exact=JSUInt31], double: [null|exact=JSNumNotInt], string: Value([exact=JSString], value: "aString"), intTwo: [null|exact=JSUInt31], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
+      /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {int: [null|exact=JSUInt31], double: [null|exact=JSNumNotInt], string: Value([exact=JSString], value: "aString"), intTwo: [null|exact=JSUInt31], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
       ['string'];
   doubleOrNull2 = union
-      /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {int: [null|exact=JSUInt31], double: [null|exact=JSNumNotInt], string: Value([exact=JSString], value: "aString"), intTwo: [null|exact=JSUInt31], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
+      /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {int: [null|exact=JSUInt31], double: [null|exact=JSNumNotInt], string: Value([exact=JSString], value: "aString"), intTwo: [null|exact=JSUInt31], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
       ['double'];
 }
 
-/*member: dictionary3:Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
+/*member: dictionary3:Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
 dynamic dictionary3 = {
   'string': "aString",
   'int': 42,
@@ -125,18 +125,18 @@
 
 /*member: intOrNull3:[null|exact=JSUInt31]*/
 dynamic intOrNull3 = dictionary3
-    /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
+    /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
     [keyI3];
 
 /*member: justNull3:[null]*/
 dynamic justNull3 = dictionary3
-    /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
+    /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
     [keyN3];
 
 /*member: test3:[null]*/
 test3() {
   knownDouble3 = dictionary3
-      /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
+      /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt], [exact=JSString], [exact=JSUInt31]), map: {string: Value([exact=JSString], value: "aString"), int: [exact=JSUInt31], double: [exact=JSNumNotInt], list: Container([exact=JSExtendableArray], element: [empty], length: 0)})*/
       [keyD3];
   // ignore: unused_local_variable
   var x = [intOrNull3, justNull3];
@@ -147,8 +147,8 @@
   A4();
 /*member: A4.foo4:[exact=JSUInt31]*/
   foo4(
-      /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSString], [exact=JSUInt31]), map: {anInt: [exact=JSUInt31], aString: Value([exact=JSString], value: "theString")})*/ value) {
-    return value /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSString], [exact=JSUInt31]), map: {anInt: [exact=JSUInt31], aString: Value([exact=JSString], value: "theString")})*/ [
+      /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSString], [exact=JSUInt31]), map: {anInt: [exact=JSUInt31], aString: Value([exact=JSString], value: "theString")})*/ value) {
+    return value /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSString], [exact=JSUInt31]), map: {anInt: [exact=JSUInt31], aString: Value([exact=JSString], value: "theString")})*/ [
         'anInt'];
   }
 }
@@ -159,7 +159,7 @@
 
 /*member: B4.foo4:[exact=JSUInt31]*/
   foo4(
-      /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSString], [exact=JSUInt31]), map: {anInt: [exact=JSUInt31], aString: Value([exact=JSString], value: "theString")})*/ value) {
+      /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSString], [exact=JSUInt31]), map: {anInt: [exact=JSUInt31], aString: Value([exact=JSString], value: "theString")})*/ value) {
     return 0;
   }
 }
@@ -180,7 +180,7 @@
       2);
 }
 
-/*member: dict5:Map([null|subclass=JsLinkedHashMap], key: [null|subclass=Object], value: [null|subclass=Object])*/
+/*member: dict5:Map([null|exact=JsLinkedHashMap], key: [null|subclass=Object], value: [null|subclass=Object])*/
 dynamic dict5 = makeMap5([1, 2]);
 
 /*member: notInt5:[null|subclass=Object]*/
@@ -189,7 +189,7 @@
 /*member: alsoNotInt5:[null|subclass=Object]*/
 dynamic alsoNotInt5 = 0;
 
-/*member: makeMap5:Map([subclass=JsLinkedHashMap], key: [null|subclass=Object], value: [null|subclass=Object])*/
+/*member: makeMap5:Map([exact=JsLinkedHashMap], key: [null|subclass=Object], value: [null|subclass=Object])*/
 makeMap5(
     /*Container([exact=JSExtendableArray], element: [exact=JSUInt31], length: 2)*/ values) {
   return {
@@ -205,14 +205,14 @@
 /*member: test5:[null]*/
 test5() {
   dict5
-      /*update: Map([null|subclass=JsLinkedHashMap], key: [null|subclass=Object], value: [null|subclass=Object])*/
+      /*update: Map([null|exact=JsLinkedHashMap], key: [null|subclass=Object], value: [null|subclass=Object])*/
       ['goo'] = 42;
   var closure =
-      /*Map([null|subclass=JsLinkedHashMap], key: [null|subclass=Object], value: [null|subclass=Object])*/
+      /*Map([null|exact=JsLinkedHashMap], key: [null|subclass=Object], value: [null|subclass=Object])*/
       () => dict5;
   notInt5 = closure()['boo'];
   alsoNotInt5 = dict5
-      /*Map([null|subclass=JsLinkedHashMap], key: [null|subclass=Object], value: [null|subclass=Object])*/
+      /*Map([null|exact=JsLinkedHashMap], key: [null|subclass=Object], value: [null|subclass=Object])*/
       ['goo'];
   print("$notInt5 and $alsoNotInt5.");
 }
diff --git a/pkg/compiler/test/inference/data/index.dart b/pkg/compiler/test/inference/data/index.dart
index 4a00271..c05e292 100644
--- a/pkg/compiler/test/inference/data/index.dart
+++ b/pkg/compiler/test/inference/data/index.dart
@@ -60,7 +60,7 @@
 mapLookupSingle() {
   var map = {0: 1};
   return map
-      /*Map([subclass=JsLinkedHashMap], key: [exact=JSUInt31], value: [null|exact=JSUInt31])*/
+      /*Map([exact=JsLinkedHashMap], key: [exact=JSUInt31], value: [null|exact=JSUInt31])*/
       [0];
 }
 
@@ -72,7 +72,7 @@
 mapLookupMultiple() {
   var map = {0: 1, 2: 3, 4: 5};
   return map
-      /*Map([subclass=JsLinkedHashMap], key: [exact=JSUInt31], value: [null|exact=JSUInt31])*/
+      /*Map([exact=JsLinkedHashMap], key: [exact=JSUInt31], value: [null|exact=JSUInt31])*/
       [2];
 }
 
@@ -84,7 +84,7 @@
 mapLookupMissing() {
   var map = {0: 1};
   return map
-      /*Map([subclass=JsLinkedHashMap], key: [exact=JSUInt31], value: [null|exact=JSUInt31])*/
+      /*Map([exact=JsLinkedHashMap], key: [exact=JSUInt31], value: [null|exact=JSUInt31])*/
       [2];
 }
 
@@ -96,7 +96,7 @@
 mapLookupMixedKeys() {
   var map = {0: 1, '': 2};
   return map
-      /*Map([subclass=JsLinkedHashMap], key: Union([exact=JSString], [exact=JSUInt31]), value: [null|exact=JSUInt31])*/
+      /*Map([exact=JsLinkedHashMap], key: Union([exact=JSString], [exact=JSUInt31]), value: [null|exact=JSUInt31])*/
       [''];
 }
 
@@ -108,7 +108,7 @@
 mapLookupMixedValues() {
   var map = {0: 1, 2: ''};
   return map
-      /*Map([subclass=JsLinkedHashMap], key: [exact=JSUInt31], value: Union(null, [exact=JSString], [exact=JSUInt31]))*/
+      /*Map([exact=JsLinkedHashMap], key: [exact=JSUInt31], value: Union(null, [exact=JSString], [exact=JSUInt31]))*/
       [2];
 }
 
@@ -120,7 +120,7 @@
 dictionaryLookupSingle() {
   var map = {'foo': 'bar'};
   return map
-      /*Dictionary([subclass=JsLinkedHashMap], key: Value([exact=JSString], value: "foo"), value: Value([null|exact=JSString], value: "bar"), map: {foo: Value([exact=JSString], value: "bar")})*/
+      /*Dictionary([exact=JsLinkedHashMap], key: Value([exact=JSString], value: "foo"), value: Value([null|exact=JSString], value: "bar"), map: {foo: Value([exact=JSString], value: "bar")})*/
       ['foo'];
 }
 
@@ -132,7 +132,7 @@
 dictionaryLookupMultiple() {
   var map = {'foo': 'bar', 'baz': 'boz'};
   return map
-      /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSString], map: {foo: Value([exact=JSString], value: "bar"), baz: Value([exact=JSString], value: "boz")})*/
+      /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSString], map: {foo: Value([exact=JSString], value: "bar"), baz: Value([exact=JSString], value: "boz")})*/
       ['baz'];
 }
 
@@ -144,7 +144,7 @@
 dictionaryLookupMissing() {
   var map = {'foo': 'bar', 'baz': 'boz'};
   return map
-      /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSString], map: {foo: Value([exact=JSString], value: "bar"), baz: Value([exact=JSString], value: "boz")})*/
+      /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSString], map: {foo: Value([exact=JSString], value: "bar"), baz: Value([exact=JSString], value: "boz")})*/
       ['unknown'];
 }
 
@@ -156,7 +156,7 @@
 intDictionaryLookupSingle() {
   var map = {'foo': 0};
   return map
-      /*Dictionary([subclass=JsLinkedHashMap], key: Value([exact=JSString], value: "foo"), value: [null|exact=JSUInt31], map: {foo: [exact=JSUInt31]})*/
+      /*Dictionary([exact=JsLinkedHashMap], key: Value([exact=JSString], value: "foo"), value: [null|exact=JSUInt31], map: {foo: [exact=JSUInt31]})*/
       ['foo'];
 }
 
diff --git a/pkg/compiler/test/inference/data/index_call.dart b/pkg/compiler/test/inference/data/index_call.dart
index 4454632..d563df2 100644
--- a/pkg/compiler/test/inference/data/index_call.dart
+++ b/pkg/compiler/test/inference/data/index_call.dart
@@ -63,9 +63,9 @@
   var a = {
     'a': {'b': 0}
   };
-  return a /*Dictionary([subclass=JsLinkedHashMap], key: Value([exact=JSString], value: "a"), value: Dictionary([null|subclass=JsLinkedHashMap], key: Value([exact=JSString], value: "b"), value: [null|exact=JSUInt31], map: {b: [exact=JSUInt31]}), map: {a: Dictionary([subclass=JsLinkedHashMap], key: Value([exact=JSString], value: "b"), value: [null|exact=JSUInt31], map: {b: [exact=JSUInt31]})})*/
+  return a /*Dictionary([exact=JsLinkedHashMap], key: Value([exact=JSString], value: "a"), value: Dictionary([null|exact=JsLinkedHashMap], key: Value([exact=JSString], value: "b"), value: [null|exact=JSUInt31], map: {b: [exact=JSUInt31]}), map: {a: Dictionary([exact=JsLinkedHashMap], key: Value([exact=JSString], value: "b"), value: [null|exact=JSUInt31], map: {b: [exact=JSUInt31]})})*/
               ['a']
-          /*Dictionary([subclass=JsLinkedHashMap], key: Value([exact=JSString], value: "b"), value: [null|exact=JSUInt31], map: {b: [exact=JSUInt31]})*/
+          /*Dictionary([exact=JsLinkedHashMap], key: Value([exact=JSString], value: "b"), value: [null|exact=JSUInt31], map: {b: [exact=JSUInt31]})*/
           ['b']
       . /*invoke: [exact=JSUInt31]*/
       abs();
@@ -77,9 +77,9 @@
   var a = {
     'a': {'b': closure}
   };
-  return a /*Dictionary([subclass=JsLinkedHashMap], key: Value([exact=JSString], value: "a"), value: Dictionary([null|subclass=JsLinkedHashMap], key: Value([exact=JSString], value: "b"), value: [null|subclass=Closure], map: {b: [subclass=Closure]}), map: {a: Dictionary([subclass=JsLinkedHashMap], key: Value([exact=JSString], value: "b"), value: [null|subclass=Closure], map: {b: [subclass=Closure]})})*/
+  return a /*Dictionary([exact=JsLinkedHashMap], key: Value([exact=JSString], value: "a"), value: Dictionary([null|exact=JsLinkedHashMap], key: Value([exact=JSString], value: "b"), value: [null|subclass=Closure], map: {b: [subclass=Closure]}), map: {a: Dictionary([exact=JsLinkedHashMap], key: Value([exact=JSString], value: "b"), value: [null|subclass=Closure], map: {b: [subclass=Closure]})})*/
           ['a']
-      /*Dictionary([subclass=JsLinkedHashMap], key: Value([exact=JSString], value: "b"), value: [null|subclass=Closure], map: {b: [subclass=Closure]})*/
+      /*Dictionary([exact=JsLinkedHashMap], key: Value([exact=JSString], value: "b"), value: [null|subclass=Closure], map: {b: [subclass=Closure]})*/
       ['b'](d: 0);
 }
 
@@ -89,7 +89,7 @@
   var a = {
     'a': [closure]
   };
-  return a /*Dictionary([subclass=JsLinkedHashMap], key: Value([exact=JSString], value: "a"), value: Container([null|exact=JSExtendableArray], element: [subclass=Closure], length: 1), map: {a: Container([exact=JSExtendableArray], element: [subclass=Closure], length: 1)})*/
+  return a /*Dictionary([exact=JsLinkedHashMap], key: Value([exact=JSString], value: "a"), value: Container([null|exact=JSExtendableArray], element: [subclass=Closure], length: 1), map: {a: Container([exact=JSExtendableArray], element: [subclass=Closure], length: 1)})*/
           ['a']
       /*Container([exact=JSExtendableArray], element: [subclass=Closure], length: 1)*/
       [0](d: 0);
diff --git a/pkg/compiler/test/inference/data/index_set.dart b/pkg/compiler/test/inference/data/index_set.dart
index 883962c..c383f3f 100644
--- a/pkg/compiler/test/inference/data/index_set.dart
+++ b/pkg/compiler/test/inference/data/index_set.dart
@@ -60,7 +60,7 @@
 mapUpdateEmpty() {
   var map = {};
   return map
-      /*update: Map([subclass=JsLinkedHashMap], key: [exact=JSUInt31], value: [null|exact=JSUInt31])*/
+      /*update: Map([exact=JsLinkedHashMap], key: [exact=JSUInt31], value: [null|exact=JSUInt31])*/
       [0] = 42;
 }
 
@@ -72,7 +72,7 @@
 mapUpdateSingle() {
   var map = {0: 1};
   return map
-      /*update: Map([subclass=JsLinkedHashMap], key: [exact=JSUInt31], value: [null|exact=JSUInt31])*/
+      /*update: Map([exact=JsLinkedHashMap], key: [exact=JSUInt31], value: [null|exact=JSUInt31])*/
       [0] = 42;
 }
 
@@ -84,7 +84,7 @@
 mapUpdateMultiple() {
   var map = {0: 1, 2: 3, 4: 5};
   return map
-      /*update: Map([subclass=JsLinkedHashMap], key: [exact=JSUInt31], value: [null|exact=JSUInt31])*/
+      /*update: Map([exact=JsLinkedHashMap], key: [exact=JSUInt31], value: [null|exact=JSUInt31])*/
       [2] = 42;
 }
 
@@ -96,7 +96,7 @@
 mapUpdateMissing() {
   var map = {0: 1};
   return map
-      /*update: Map([subclass=JsLinkedHashMap], key: [exact=JSUInt31], value: [null|exact=JSUInt31])*/
+      /*update: Map([exact=JsLinkedHashMap], key: [exact=JSUInt31], value: [null|exact=JSUInt31])*/
       [2] = 42;
 }
 
@@ -108,7 +108,7 @@
 mapUpdateMixedKeys() {
   dynamic map = {'': 2};
   return map
-      /*update: Map([subclass=JsLinkedHashMap], key: Union([exact=JSString], [exact=JSUInt31]), value: [null|exact=JSUInt31])*/
+      /*update: Map([exact=JsLinkedHashMap], key: Union([exact=JSString], [exact=JSUInt31]), value: [null|exact=JSUInt31])*/
       [0] = 42;
 }
 
@@ -120,7 +120,7 @@
 mapUpdateMixedValues() {
   dynamic map = {2: ''};
   return map
-      /*update: Map([subclass=JsLinkedHashMap], key: [exact=JSUInt31], value: Union(null, [exact=JSString], [exact=JSUInt31]))*/
+      /*update: Map([exact=JsLinkedHashMap], key: [exact=JSUInt31], value: Union(null, [exact=JSString], [exact=JSUInt31]))*/
       [2] = 42;
 }
 
@@ -132,7 +132,7 @@
 dictionaryUpdateEmpty() {
   var map = {};
   return map
-      /*update: Dictionary([subclass=JsLinkedHashMap], key: Value([exact=JSString], value: "foo"), value: Value([null|exact=JSString], value: "bar"), map: {foo: Value([null|exact=JSString], value: "bar")})*/
+      /*update: Dictionary([exact=JsLinkedHashMap], key: Value([exact=JSString], value: "foo"), value: Value([null|exact=JSString], value: "bar"), map: {foo: Value([null|exact=JSString], value: "bar")})*/
       ['foo'] = 'bar';
 }
 
@@ -144,7 +144,7 @@
 dictionaryUpdateSingle() {
   var map = {'foo': 'bar'};
   return map
-      /*update: Dictionary([subclass=JsLinkedHashMap], key: Value([exact=JSString], value: "foo"), value: [null|exact=JSString], map: {foo: [exact=JSString]})*/
+      /*update: Dictionary([exact=JsLinkedHashMap], key: Value([exact=JSString], value: "foo"), value: [null|exact=JSString], map: {foo: [exact=JSString]})*/
       ['foo'] = 'boz';
 }
 
@@ -156,7 +156,7 @@
 dictionaryReUpdateSingle() {
   var map = {'foo': 'bar'};
   return map
-      /*update: Dictionary([subclass=JsLinkedHashMap], key: Value([exact=JSString], value: "foo"), value: Value([null|exact=JSString], value: "bar"), map: {foo: Value([exact=JSString], value: "bar")})*/
+      /*update: Dictionary([exact=JsLinkedHashMap], key: Value([exact=JSString], value: "foo"), value: Value([null|exact=JSString], value: "bar"), map: {foo: Value([exact=JSString], value: "bar")})*/
       ['foo'] = 'bar';
 }
 
@@ -168,7 +168,7 @@
 dictionaryUpdateMultiple() {
   var map = {'foo': 'bar'};
   return map
-      /*update: Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSString], map: {foo: Value([exact=JSString], value: "bar"), baz: Value([null|exact=JSString], value: "boz")})*/
+      /*update: Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSString], map: {foo: Value([exact=JSString], value: "bar"), baz: Value([null|exact=JSString], value: "boz")})*/
       ['baz'] = 'boz';
 }
 
@@ -180,7 +180,7 @@
 intDictionaryUpdateSingle() {
   var map = {};
   return map
-      /*update: Dictionary([subclass=JsLinkedHashMap], key: Value([exact=JSString], value: "foo"), value: [null|exact=JSUInt31], map: {foo: [null|exact=JSUInt31]})*/
+      /*update: Dictionary([exact=JsLinkedHashMap], key: Value([exact=JSString], value: "foo"), value: [null|exact=JSUInt31], map: {foo: [null|exact=JSUInt31]})*/
       ['foo'] = 0;
 }
 
diff --git a/pkg/compiler/test/inference/data/map_tracer_keys.dart b/pkg/compiler/test/inference/data/map_tracer_keys.dart
index beedfbf..1e70a9e 100644
--- a/pkg/compiler/test/inference/data/map_tracer_keys.dart
+++ b/pkg/compiler/test/inference/data/map_tracer_keys.dart
@@ -29,16 +29,16 @@
 test1() {
   var theMap = {'a': 2.2, 'b': 3.3, 'c': 4.4};
   theMap
-      /*update: Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSNumNotInt], map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: [null|exact=JSNumNotInt]})*/
+      /*update: Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSNumNotInt], map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: [null|exact=JSNumNotInt]})*/
       ['d'] = 5.5;
   /*iterator: [exact=LinkedHashMapKeyIterable]*/
   /*current: [exact=LinkedHashMapKeyIterator]*/
   /*moveNext: [exact=LinkedHashMapKeyIterator]*/
   for (var key in theMap.
-      /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSNumNotInt], map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: [null|exact=JSNumNotInt]})*/
+      /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSNumNotInt], map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: [null|exact=JSNumNotInt]})*/
       keys) {
     aDouble1 = theMap
-        /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSNumNotInt], map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: [null|exact=JSNumNotInt]})*/
+        /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSNumNotInt], map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: [null|exact=JSNumNotInt]})*/
         [key];
   }
   // We have to reference it somewhere, so that it always gets resolved.
@@ -60,16 +60,16 @@
 test2() {
   dynamic theMap = {'a': 2.2, 'b': 3.3, 'c': 4.4};
   theMap
-      /*update: Map([subclass=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSNumNotInt])*/
+      /*update: Map([exact=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSNumNotInt])*/
       [aList2] = 5.5;
   /*iterator: [exact=LinkedHashMapKeyIterable]*/
   /*current: [exact=LinkedHashMapKeyIterator]*/
   /*moveNext: [exact=LinkedHashMapKeyIterator]*/
   for (var key in theMap.
-      /*Map([subclass=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSNumNotInt])*/
+      /*Map([exact=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSNumNotInt])*/
       keys) {
     aDouble2 = theMap
-        /*Map([subclass=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSNumNotInt])*/
+        /*Map([exact=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSNumNotInt])*/
         [key];
   }
   // We have to reference it somewhere, so that it always gets resolved.
@@ -91,16 +91,16 @@
 test3() {
   dynamic theMap = <dynamic, dynamic>{'a': 2.2, 'b': 3.3, 'c': 4.4};
   theMap
-      /*update: Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt]), map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: Container([null|exact=JSExtendableArray], element: [exact=JSUInt31], length: 1)})*/
+      /*update: Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt]), map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: Container([null|exact=JSExtendableArray], element: [exact=JSUInt31], length: 1)})*/
       ['d'] = aList3;
   /*iterator: [exact=LinkedHashMapKeyIterable]*/
   /*current: [exact=LinkedHashMapKeyIterator]*/
   /*moveNext: [exact=LinkedHashMapKeyIterator]*/
   for (var key in theMap.
-      /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt]), map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: Container([null|exact=JSExtendableArray], element: [exact=JSUInt31], length: 1)})*/
+      /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt]), map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: Container([null|exact=JSExtendableArray], element: [exact=JSUInt31], length: 1)})*/
       keys) {
     aDouble3 = theMap
-        /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt]), map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: Container([null|exact=JSExtendableArray], element: [exact=JSUInt31], length: 1)})*/
+        /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt]), map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: Container([null|exact=JSExtendableArray], element: [exact=JSUInt31], length: 1)})*/
         [key];
   }
   // We have to reference it somewhere, so that it always gets resolved.
@@ -125,10 +125,10 @@
   /*current: [exact=LinkedHashMapKeyIterator]*/
   /*moveNext: [exact=LinkedHashMapKeyIterator]*/
   for (var key in theMap.
-      /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSNumNotInt], map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: [exact=JSNumNotInt]})*/
+      /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSNumNotInt], map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: [exact=JSNumNotInt]})*/
       keys) {
     aDouble4 = theMap
-        /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSNumNotInt], map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: [exact=JSNumNotInt]})*/
+        /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: [null|exact=JSNumNotInt], map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: [exact=JSNumNotInt]})*/
         [key];
   }
   // We have to reference it somewhere, so that it always gets resolved.
@@ -153,10 +153,10 @@
   /*current: [exact=LinkedHashMapKeyIterator]*/
   /*moveNext: [exact=LinkedHashMapKeyIterator]*/
   for (var key in theMap.
-      /*Map([subclass=JsLinkedHashMap], key: Union([exact=JSExtendableArray], [exact=JSString]), value: [null|exact=JSNumNotInt])*/
+      /*Map([exact=JsLinkedHashMap], key: Union([exact=JSExtendableArray], [exact=JSString]), value: [null|exact=JSNumNotInt])*/
       keys) {
     aDouble5 = theMap
-        /*Map([subclass=JsLinkedHashMap], key: Union([exact=JSExtendableArray], [exact=JSString]), value: [null|exact=JSNumNotInt])*/
+        /*Map([exact=JsLinkedHashMap], key: Union([exact=JSExtendableArray], [exact=JSString]), value: [null|exact=JSNumNotInt])*/
         [key];
   }
   // We have to reference it somewhere, so that it always gets resolved.
@@ -180,10 +180,10 @@
   /*current: [exact=LinkedHashMapKeyIterator]*/
   /*moveNext: [exact=LinkedHashMapKeyIterator]*/
   for (var key in theMap.
-      /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt]), map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: Container([exact=JSExtendableArray], element: [exact=JSUInt31], length: 1)})*/
+      /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt]), map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: Container([exact=JSExtendableArray], element: [exact=JSUInt31], length: 1)})*/
       keys) {
     aDouble6 = theMap
-        /*Dictionary([subclass=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt]), map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: Container([exact=JSExtendableArray], element: [exact=JSUInt31], length: 1)})*/
+        /*Dictionary([exact=JsLinkedHashMap], key: [exact=JSString], value: Union(null, [exact=JSExtendableArray], [exact=JSNumNotInt]), map: {a: [exact=JSNumNotInt], b: [exact=JSNumNotInt], c: [exact=JSNumNotInt], d: Container([exact=JSExtendableArray], element: [exact=JSUInt31], length: 1)})*/
         [key];
   }
   // We have to reference it somewhere, so that it always gets resolved.
diff --git a/pkg/compiler/test/inference/data/no_such_method4.dart b/pkg/compiler/test/inference/data/no_such_method4.dart
index 0538869..2cd61c1 100644
--- a/pkg/compiler/test/inference/data/no_such_method4.dart
+++ b/pkg/compiler/test/inference/data/no_such_method4.dart
@@ -13,13 +13,13 @@
 
 /*member: B.:[exact=B]*/
 class B extends A {
-  /*member: B.foo:Dictionary([subclass=JsLinkedHashMap], key: [empty], value: [null], map: {})*/ foo() =>
+  /*member: B.foo:Dictionary([exact=JsLinkedHashMap], key: [empty], value: [null], map: {})*/ foo() =>
       {};
 }
 
 /*member: C.:[exact=C]*/
 class C extends B {
-  /*member: C.foo:Dictionary([subclass=JsLinkedHashMap], key: [empty], value: [null], map: {})*/ foo() =>
+  /*member: C.foo:Dictionary([exact=JsLinkedHashMap], key: [empty], value: [null], map: {})*/ foo() =>
       {};
 }
 
@@ -34,22 +34,22 @@
   return e. /*invoke: [exact=A]*/ foo();
 }
 
-/*member: test2:Dictionary([subclass=JsLinkedHashMap], key: [empty], value: [null], map: {})*/
+/*member: test2:Dictionary([exact=JsLinkedHashMap], key: [empty], value: [null], map: {})*/
 test2() => a. /*invoke: [null|subclass=B]*/ foo();
 
-/*member: test3:Dictionary([subclass=JsLinkedHashMap], key: [empty], value: [null], map: {})*/
+/*member: test3:Dictionary([exact=JsLinkedHashMap], key: [empty], value: [null], map: {})*/
 test3() => new B(). /*invoke: [exact=B]*/ foo();
 
-/*member: test4:Dictionary([subclass=JsLinkedHashMap], key: [empty], value: [null], map: {})*/
+/*member: test4:Dictionary([exact=JsLinkedHashMap], key: [empty], value: [null], map: {})*/
 test4() => new C(). /*invoke: [exact=C]*/ foo();
 
-/*member: test5:Dictionary([subclass=JsLinkedHashMap], key: [empty], value: [null], map: {})*/
+/*member: test5:Dictionary([exact=JsLinkedHashMap], key: [empty], value: [null], map: {})*/
 test5() {
   dynamic e = (a ? new A() : new B());
   return e. /*invoke: [subclass=A]*/ foo();
 }
 
-/*member: test6:Dictionary([subclass=JsLinkedHashMap], key: [empty], value: [null], map: {})*/
+/*member: test6:Dictionary([exact=JsLinkedHashMap], key: [empty], value: [null], map: {})*/
 test6() => (a ? new B() : new C()). /*invoke: [subclass=B]*/ foo();
 
 /*member: main:[null]*/
diff --git a/pkg/compiler/test/rti/data/map_literal.dart b/pkg/compiler/test/rti/data/map_literal.dart
index 1d91a1b..988f06e 100644
--- a/pkg/compiler/test/rti/data/map_literal.dart
+++ b/pkg/compiler/test/rti/data/map_literal.dart
@@ -11,7 +11,7 @@
 /*spec.class: global#LinkedHashMap:deps=[Map],direct,explicit=[LinkedHashMap<LinkedHashMap.K,LinkedHashMap.V>],implicit=[LinkedHashMap.K,LinkedHashMap.V],needsArgs*/
 
 /*prod.class: global#JsLinkedHashMap:deps=[LinkedHashMap]*/
-/*spec.class: global#JsLinkedHashMap:deps=[LinkedHashMap],direct,explicit=[JsLinkedHashMap,JsLinkedHashMap.K,JsLinkedHashMap.V,void Function(JsLinkedHashMap.K,JsLinkedHashMap.V)],implicit=[JsLinkedHashMap.K,JsLinkedHashMap.V],needsArgs*/
+/*spec.class: global#JsLinkedHashMap:deps=[LinkedHashMap],direct,explicit=[JsLinkedHashMap,JsLinkedHashMap.K,JsLinkedHashMap.V,void Function(JsLinkedHashMap.K,JsLinkedHashMap.V)],implicit=[JsLinkedHashMap.K],needsArgs*/
 
 /*prod.class: global#double:*/
 /*spec.class: global#double:implicit=[double]*/
diff --git a/pkg/compiler/test/rti/data/map_to_set.dart b/pkg/compiler/test/rti/data/map_to_set.dart
index 79f0f2a..4c870c3 100644
--- a/pkg/compiler/test/rti/data/map_to_set.dart
+++ b/pkg/compiler/test/rti/data/map_to_set.dart
@@ -11,7 +11,7 @@
 /*spec.class: global#LinkedHashMap:deps=[Map],direct,explicit=[LinkedHashMap<LinkedHashMap.K,LinkedHashMap.V>],implicit=[LinkedHashMap.K,LinkedHashMap.V],needsArgs*/
 
 /*prod.class: global#JsLinkedHashMap:deps=[LinkedHashMap],implicit=[JsLinkedHashMap.K],needsArgs*/
-/*spec.class: global#JsLinkedHashMap:deps=[LinkedHashMap],direct,explicit=[JsLinkedHashMap,JsLinkedHashMap.K,JsLinkedHashMap.V,void Function(JsLinkedHashMap.K,JsLinkedHashMap.V)],implicit=[JsLinkedHashMap.K,JsLinkedHashMap.V],needsArgs*/
+/*spec.class: global#JsLinkedHashMap:deps=[LinkedHashMap],direct,explicit=[JsLinkedHashMap,JsLinkedHashMap.K,JsLinkedHashMap.V,void Function(JsLinkedHashMap.K,JsLinkedHashMap.V)],implicit=[JsLinkedHashMap.K],needsArgs*/
 
 /*prod.class: global#double:*/
 /*spec.class: global#double:implicit=[double]*/
diff --git a/sdk/lib/_internal/js_runtime/lib/collection_patch.dart b/sdk/lib/_internal/js_runtime/lib/collection_patch.dart
index b01ebb6..8db9d2a 100644
--- a/sdk/lib/_internal/js_runtime/lib/collection_patch.dart
+++ b/sdk/lib/_internal/js_runtime/lib/collection_patch.dart
@@ -17,8 +17,6 @@
 
 import 'dart:_internal' hide Symbol;
 
-const _USE_ES6_MAPS = const bool.fromEnvironment("dart2js.use.es6.maps");
-
 const int _mask30 = 0x3fffffff; // Low 30 bits.
 
 @patch
@@ -509,13 +507,13 @@
     if (isValidKey == null) {
       if (hashCode == null) {
         if (equals == null) {
-          return new JsLinkedHashMap<K, V>.es6();
+          return new JsLinkedHashMap<K, V>();
         }
         hashCode = _defaultHashCode;
       } else {
         if (identical(identityHashCode, hashCode) &&
             identical(identical, equals)) {
-          return new _LinkedIdentityHashMap<K, V>.es6();
+          return new _LinkedIdentityHashMap<K, V>();
         }
         if (equals == null) {
           equals = _defaultEquals;
@@ -533,12 +531,12 @@
   }
 
   @patch
-  factory LinkedHashMap.identity() = _LinkedIdentityHashMap<K, V>.es6;
+  factory LinkedHashMap.identity() = _LinkedIdentityHashMap<K, V>;
 
   // Private factory constructor called by generated code for map literals.
   @pragma('dart2js:noInline')
   factory LinkedHashMap._literal(List keyValuePairs) {
-    return fillLiteralMap(keyValuePairs, new JsLinkedHashMap<K, V>.es6());
+    return fillLiteralMap(keyValuePairs, new JsLinkedHashMap<K, V>());
   }
 
   // Private factory constructor called by generated code for map literals.
@@ -546,7 +544,7 @@
   @pragma('dart2js:noInline')
   @pragma('dart2js:noSideEffects')
   factory LinkedHashMap._empty() {
-    return new JsLinkedHashMap<K, V>.es6();
+    return new JsLinkedHashMap<K, V>();
   }
 
   // Private factory static function called by generated code for map literals.
@@ -564,17 +562,6 @@
 }
 
 class _LinkedIdentityHashMap<K, V> extends JsLinkedHashMap<K, V> {
-  static bool get _supportsEs6Maps {
-    return JS('returns:bool;depends:none;effects:none;throws:never;gvn:true',
-        'typeof Map != "undefined"');
-  }
-
-  factory _LinkedIdentityHashMap.es6() {
-    return (_USE_ES6_MAPS && _LinkedIdentityHashMap._supportsEs6Maps)
-        ? new _Es6LinkedIdentityHashMap<K, V>()
-        : new _LinkedIdentityHashMap<K, V>();
-  }
-
   _LinkedIdentityHashMap();
 
   int internalComputeHashCode(var key) {
@@ -595,161 +582,6 @@
   }
 }
 
-class _Es6LinkedIdentityHashMap<K, V> extends _LinkedIdentityHashMap<K, V>
-    implements InternalMap {
-  final _map;
-  int _modifications = 0;
-
-  _Es6LinkedIdentityHashMap() : _map = JS('var', 'new Map()');
-
-  int get length => JS('int', '#.size', _map);
-  bool get isEmpty => length == 0;
-  bool get isNotEmpty => !isEmpty;
-
-  Iterable<K> get keys => new _Es6MapIterable<K>(this, true);
-
-  Iterable<V> get values => new _Es6MapIterable<V>(this, false);
-
-  bool containsKey(Object? key) {
-    return JS('bool', '#.has(#)', _map, key);
-  }
-
-  bool containsValue(Object? value) {
-    return values.any((each) => each == value);
-  }
-
-  void addAll(Map<K, V> other) {
-    other.forEach((K key, V value) {
-      this[key] = value;
-    });
-  }
-
-  V? operator [](Object? key) {
-    return JS('var', '#.get(#)', _map, key);
-  }
-
-  void operator []=(K key, V value) {
-    JS('var', '#.set(#, #)', _map, key, value);
-    _modified();
-  }
-
-  V putIfAbsent(K key, V ifAbsent()) {
-    if (containsKey(key)) return this[key] as V;
-    V value = ifAbsent();
-    this[key] = value;
-    return value;
-  }
-
-  V? remove(Object? key) {
-    V? value = this[key];
-    JS('bool', '#.delete(#)', _map, key);
-    _modified();
-    return value;
-  }
-
-  void clear() {
-    JS('void', '#.clear()', _map);
-    _modified();
-  }
-
-  void forEach(void action(K key, V value)) {
-    var jsEntries = JS('var', '#.entries()', _map);
-    int modifications = _modifications;
-    while (true) {
-      var next = JS('var', '#.next()', jsEntries);
-      bool done = JS('bool', '#.done', next);
-      if (done) break;
-      var entry = JS('var', '#.value', next);
-      var key = JS('var', '#[0]', entry);
-      var value = JS('var', '#[1]', entry);
-      action(key, value);
-      if (modifications != _modifications) {
-        throw new ConcurrentModificationError(this);
-      }
-    }
-  }
-
-  void _modified() {
-    // Value cycles after 2^30 modifications so that modification counts are
-    // always unboxed (Smi) values. Modification detection will be missed if you
-    // make exactly some multiple of 2^30 modifications between advances of an
-    // iterator.
-    _modifications = _mask30 & (_modifications + 1);
-  }
-}
-
-class _Es6MapIterable<E> extends EfficientLengthIterable<E> {
-  final _Es6LinkedIdentityHashMap _map;
-  final bool _isKeys;
-
-  _Es6MapIterable(this._map, this._isKeys);
-
-  int get length => _map.length;
-  bool get isEmpty => _map.isEmpty;
-
-  Iterator<E> get iterator =>
-      new _Es6MapIterator<E>(_map, _map._modifications, _isKeys);
-
-  bool contains(Object? element) => _map.containsKey(element);
-
-  void forEach(void f(E element)) {
-    var jsIterator;
-    if (_isKeys) {
-      jsIterator = JS('var', '#.keys()', _map._map);
-    } else {
-      jsIterator = JS('var', '#.values()', _map._map);
-    }
-    int modifications = _map._modifications;
-    while (true) {
-      var next = JS('var', '#.next()', jsIterator);
-      bool done = JS('bool', '#.done', next);
-      if (done) break;
-      var value = JS('var', '#.value', next);
-      f(value);
-      if (modifications != _map._modifications) {
-        throw new ConcurrentModificationError(_map);
-      }
-    }
-  }
-}
-
-class _Es6MapIterator<E> implements Iterator<E> {
-  final _Es6LinkedIdentityHashMap _map;
-  final int _modifications;
-  final bool _isKeys;
-  var _jsIterator;
-  var _next;
-  E? _current;
-  bool _done = false;
-
-  _Es6MapIterator(this._map, this._modifications, this._isKeys) {
-    if (_isKeys) {
-      _jsIterator = JS('var', '#.keys()', _map._map);
-    } else {
-      _jsIterator = JS('var', '#.values()', _map._map);
-    }
-  }
-
-  E get current => _current as E;
-
-  bool moveNext() {
-    if (_modifications != _map._modifications) {
-      throw new ConcurrentModificationError(_map);
-    }
-    if (_done) return false;
-    _next = JS('var', '#.next()', _jsIterator);
-    bool done = JS('bool', '#.done', _next);
-    if (done) {
-      _current = null;
-      _done = true;
-      return false;
-    } else {
-      _current = JS('var', '#.value', _next);
-      return true;
-    }
-  }
-}
-
 // TODO(floitsch): use ES6 maps when available.
 class _LinkedCustomHashMap<K, V> extends JsLinkedHashMap<K, V> {
   final _Equality<K> _equals;
diff --git a/sdk/lib/_internal/js_runtime/lib/core_patch.dart b/sdk/lib/_internal/js_runtime/lib/core_patch.dart
index 6d4d129..9579a76 100644
--- a/sdk/lib/_internal/js_runtime/lib/core_patch.dart
+++ b/sdk/lib/_internal/js_runtime/lib/core_patch.dart
@@ -478,7 +478,7 @@
   factory Map.unmodifiable(Map other) = ConstantMap<K, V>.from;
 
   @patch
-  factory Map() = JsLinkedHashMap<K, V>.es6;
+  factory Map() = JsLinkedHashMap<K, V>;
 }
 
 @patch
diff --git a/sdk/lib/_internal/js_runtime/lib/linked_hash_map.dart b/sdk/lib/_internal/js_runtime/lib/linked_hash_map.dart
index fdf9d23..bd8533a 100644
--- a/sdk/lib/_internal/js_runtime/lib/linked_hash_map.dart
+++ b/sdk/lib/_internal/js_runtime/lib/linked_hash_map.dart
@@ -7,8 +7,6 @@
 
 part of _js_helper;
 
-const _USE_ES6_MAPS = const bool.fromEnvironment("dart2js.use.es6.maps");
-
 class JsLinkedHashMap<K, V> extends MapBase<K, V>
     implements LinkedHashMap<K, V>, InternalMap {
   int _length = 0;
@@ -35,21 +33,8 @@
   // iterated over.
   int _modifications = 0;
 
-  static bool get _supportsEs6Maps {
-    return JS('returns:bool;depends:none;effects:none;throws:never;gvn:true',
-        'typeof Map != "undefined"');
-  }
-
   JsLinkedHashMap();
 
-  /// If ES6 Maps are available returns a linked hash-map backed by an ES6 Map.
-  @pragma('dart2js:tryInline')
-  factory JsLinkedHashMap.es6() {
-    return (_USE_ES6_MAPS && JsLinkedHashMap._supportsEs6Maps)
-        ? new Es6LinkedHashMap<K, V>()
-        : new JsLinkedHashMap<K, V>();
-  }
-
   int get length => _length;
   bool get isEmpty => _length == 0;
   bool get isNotEmpty => !isEmpty;
@@ -342,38 +327,6 @@
   }
 }
 
-class Es6LinkedHashMap<K, V> extends JsLinkedHashMap<K, V> {
-  @override
-  LinkedHashMapCell? _getTableCell(var table, var key) {
-    return JS('var', '#.get(#)', table, key);
-  }
-
-  @override
-  List<LinkedHashMapCell>? _getTableBucket(var table, var key) {
-    return JS('var', '#.get(#)', table, key);
-  }
-
-  @override
-  void _setTableEntry(var table, var key, var value) {
-    JS('void', '#.set(#, #)', table, key, value);
-  }
-
-  @override
-  void _deleteTableEntry(var table, var key) {
-    JS('void', '#.delete(#)', table, key);
-  }
-
-  @override
-  bool _containsTableEntry(var table, var key) {
-    return JS('bool', '#.has(#)', table, key);
-  }
-
-  @override
-  _newHashTable() {
-    return JS('var', 'new Map()');
-  }
-}
-
 class LinkedHashMapCell {
   final dynamic hashMapCellKey;
   dynamic hashMapCellValue;