Remaining code changes for Dart 2.0 SDK roll. (#13741)

* Remaining code changes for Dart 2.0 SDK roll

dev/bots/test.dart

@@ -498,10 +498,10 @@ Future<Null> _verifyGeneratedPluginRegistrants(String flutterRoot) async {
   final Set<String> outOfDate = new Set<String>();
 
   for (String package in packageToRegistrants.keys) {
-    final Map<File, String> fileToContent = new Map<File, String>.fromIterable(packageToRegistrants[package],
-      key: (File f) => f,
-      value: (File f) => f.readAsStringSync(),
-    );
+    final Map<File, String> fileToContent = <File, String>{};
+    for(File f in packageToRegistrants[package]) {
+      fileToContent[f] = f.readAsStringSync();
+    }
     await _runCommand(flutter, <String>['inject-plugins'],
       workingDirectory: package,
       printOutput: false,

packages/flutter/lib/src/widgets/navigator.dart

@@ -552,7 +552,8 @@ class Navigator extends StatefulWidget {
   ///
   /// Returns a [Future] that completes to the `result` value passed to [pop]
   /// when the pushed route is popped off the navigator.
-  static Future<dynamic> push(BuildContext context, Route<dynamic> route) {
+  @optionalTypeArgs
+  static Future<T> push<T>(BuildContext context, Route<T> route) {
     return Navigator.of(context).push(route);
   }
 
@@ -913,7 +914,7 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin {
   ///
   /// Returns a [Future] that completes to the `result` value passed to [pop]
   /// when the pushed route is popped off the navigator.
-  Future<dynamic> push(Route<dynamic> route) {
+  Future<Object> push(Route<Object> route) {
     assert(!_debugLocked);
     assert(() { _debugLocked = true; return true; }());
     assert(route != null);

packages/flutter_test/lib/src/matchers.dart

@@ -592,7 +592,20 @@ class _HasGoodToStringDeep extends Matcher {
 /// sets of value for which a metric space is defined.
 typedef num DistanceFunction<T>(T a, T b);
 
-const Map<Type, DistanceFunction<dynamic>> _kStandardDistanceFunctions = const <Type, DistanceFunction<dynamic>>{
+/// The type of a union of instances of [DistanceFunction<T>] for various types
+/// T.
+///
+/// This type is used to describe a collection of [DistanceFunction<T>]
+/// functions which have (potentially) unrelated argument types.  Since the
+/// argument types of the functions may be unrelated, the only thing that the
+/// type system can statically assume about them is that they accept null (since
+/// all types in Dart are nullable).
+///
+/// Calling an instance of this type must either be done dynamically, or by
+/// first casting it to a [DistanceFunction<T>] for some concrete T.
+typedef num AnyDistanceFunction(Null a, Null b);
+
+const Map<Type, AnyDistanceFunction> _kStandardDistanceFunctions = const <Type, AnyDistanceFunction>{
   Color: _maxComponentColorDistance,
   Offset: _offsetDistance,
   int: _intDistance,