Fix all strong-mode warnings. R=jmesserly@google.com Review URL: https://codereview.chromium.org//1948223002 .

diff --git a/pkgs/yaml/.analysis_options b/pkgs/yaml/.analysis_options
new file mode 100644
index 0000000..a10d4c5
--- /dev/null
+++ b/pkgs/yaml/.analysis_options

@@ -0,0 +1,2 @@
+analyzer:
+  strong-mode: true

diff --git a/pkgs/yaml/CHANGELOG.md b/pkgs/yaml/CHANGELOG.md
index bb4d88e..e1a43b2 100644
--- a/pkgs/yaml/CHANGELOG.md
+++ b/pkgs/yaml/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 2.1.9
+
+* Fix all strong-mode warnings.
+
 ## 2.1.8
 
 * Remove the dependency on `path`, since we don't actually import it.

diff --git a/pkgs/yaml/lib/src/equality.dart b/pkgs/yaml/lib/src/equality.dart
index a6874cb..846f716 100644
--- a/pkgs/yaml/lib/src/equality.dart
+++ b/pkgs/yaml/lib/src/equality.dart

@@ -9,7 +9,8 @@
 import 'yaml_node.dart';
 
 /// Returns a [Map] that compares its keys based on [deepEquals].
-Map deepEqualsMap() => new HashMap(equals: deepEquals, hashCode: deepHashCode);
+Map/*<K, V>*/ deepEqualsMap/*<K, V>*/() =>
+    new HashMap(equals: deepEquals, hashCode: deepHashCode);
 
 /// Returns whether two objects are structurally equivalent.
 ///

diff --git a/pkgs/yaml/lib/src/loader.dart b/pkgs/yaml/lib/src/loader.dart
index fee7769..ea6eb99 100644
--- a/pkgs/yaml/lib/src/loader.dart
+++ b/pkgs/yaml/lib/src/loader.dart

@@ -147,7 +147,7 @@
       throw new YamlException("Invalid tag for mapping.", firstEvent.span);
     }
 
-    var children = deepEqualsMap();
+    var children = deepEqualsMap/*<dynamic, YamlNode>*/();
     var node = new YamlMap.internal(
         children, firstEvent.span, firstEvent.style);
     _registerAnchor(firstEvent.anchor, node);

diff --git a/pkgs/yaml/pubspec.yaml b/pkgs/yaml/pubspec.yaml
index ad89309..87ddd5b 100644
--- a/pkgs/yaml/pubspec.yaml
+++ b/pkgs/yaml/pubspec.yaml

@@ -1,5 +1,5 @@
 name: yaml
-version: 2.1.8
+version: 2.1.9
 author: "Dart Team <misc@dartlang.org>"
 homepage: https://github.com/dart-lang/yaml
 description: A parser for YAML.

diff --git a/pkgs/yaml/test/yaml_test.dart b/pkgs/yaml/test/yaml_test.dart
index d2f5d19..153af5e 100644
--- a/pkgs/yaml/test/yaml_test.dart
+++ b/pkgs/yaml/test/yaml_test.dart

@@ -57,14 +57,14 @@
 - foo:
     bar
 - 123
-""");
+""") as YamlList;
 
     expect(yaml.span.start.line, equals(0));
     expect(yaml.span.start.column, equals(0));
     expect(yaml.span.end.line, equals(3));
     expect(yaml.span.end.column, equals(0));
 
-    var map = yaml.nodes.first;
+    var map = yaml.nodes.first as YamlMap;
     expect(map.span.start.line, equals(0));
     expect(map.span.start.column, equals(2));
     expect(map.span.end.line, equals(2));