Fix all strong mode warnings.

R=tjblasi@google.com

Review URL: https://codereview.chromium.org//1830053002 .

pkgs/stack_trace/.analysis_options

diff --git a/pkgs/stack_trace/.analysis_options b/pkgs/stack_trace/.analysis_options
new file mode 100644
index 0000000..a10d4c5
--- /dev/null
+++ b/pkgs/stack_trace/.analysis_options
@@ -0,0 +1,2 @@
+analyzer:
+  strong-mode: true

pkgs/stack_trace/CHANGELOG.md

diff --git a/pkgs/stack_trace/CHANGELOG.md b/pkgs/stack_trace/CHANGELOG.md
index 66c1108..8ed5060 100644
--- a/pkgs/stack_trace/CHANGELOG.md
+++ b/pkgs/stack_trace/CHANGELOG.md
@@ -1,6 +1,10 @@
+## 1.6.2
+
+* Fix all strong mode warnings.
+
 ## 1.6.1
 
-* Use `StacktTrace.current` in Dart SDK 1.14 to get the current stack trace.
+* Use `StackTrace.current` in Dart SDK 1.14 to get the current stack trace.
 
 ## 1.6.0
 

pkgs/stack_trace/lib/src/chain.dart

diff --git a/pkgs/stack_trace/lib/src/chain.dart b/pkgs/stack_trace/lib/src/chain.dart
index c282387..b6f36d2 100644
--- a/pkgs/stack_trace/lib/src/chain.dart
+++ b/pkgs/stack_trace/lib/src/chain.dart
@@ -193,7 +193,7 @@
   ///
   /// The trace version of a chain is just the concatenation of all the traces
   /// in the chain.
-  Trace toTrace() => new Trace(flatten(traces.map((trace) => trace.frames)));
+  Trace toTrace() => new Trace(traces.expand((trace) => trace.frames));
 
   String toString() {
     // Figure out the longest path so we know how much to pad.

pkgs/stack_trace/lib/src/trace.dart

diff --git a/pkgs/stack_trace/lib/src/trace.dart b/pkgs/stack_trace/lib/src/trace.dart
index 927a167..0a7f320 100644
--- a/pkgs/stack_trace/lib/src/trace.dart
+++ b/pkgs/stack_trace/lib/src/trace.dart
@@ -257,7 +257,7 @@
       };
     }
 
-    var newFrames = [];
+    var newFrames = <Frame>[];
     for (var frame in frames.reversed) {
       if (frame is UnparsedFrame || !predicate(frame)) {
         newFrames.add(frame);

pkgs/stack_trace/lib/src/utils.dart

diff --git a/pkgs/stack_trace/lib/src/utils.dart b/pkgs/stack_trace/lib/src/utils.dart
index 5781d5f..710abdc 100644
--- a/pkgs/stack_trace/lib/src/utils.dart
+++ b/pkgs/stack_trace/lib/src/utils.dart
@@ -19,20 +19,3 @@
 
   return result.toString();
 }
-
-/// Flattens nested lists inside an iterable into a single list containing only
-/// non-list elements.
-List flatten(Iterable nested) {
-  var result = [];
-  helper(list) {
-    for (var element in list) {
-      if (element is List) {
-        helper(element);
-      } else {
-        result.add(element);
-      }
-    }
-  }
-  helper(nested);
-  return result;
-}

pkgs/stack_trace/pubspec.yaml

diff --git a/pkgs/stack_trace/pubspec.yaml b/pkgs/stack_trace/pubspec.yaml
index 1c180cf..465011b 100644
--- a/pkgs/stack_trace/pubspec.yaml
+++ b/pkgs/stack_trace/pubspec.yaml
@@ -7,7 +7,7 @@
 #
 # When the major version is upgraded, you *must* update that version constraint
 # in pub to stay in sync with this.
-version: 1.6.2-dev
+version: 1.6.2
 author: "Dart Team <misc@dartlang.org>"
 homepage: http://github.com/dart-lang/stack_trace
 description: >