Starting making dart2js strong mode clean.

pkg/compiler/lib/src/native/behavior.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import '../common.dart';
 import '../common/backend_api.dart' show ForeignResolver;
 import '../common/resolution.dart' show ParsingContext, Resolution;
 import '../compiler.dart' show Compiler;
 import '../constants/values.dart';
 import '../common_elements.dart' show CommonElements;
@@ skipping 505 matching lines @@
       DiagnosticReporter reporter,
       ParsingContext parsing,
       CommonElements commonElements,
       ForeignResolver resolver) {
     var argNodes = jsCall.arguments;
     if (argNodes.isEmpty || argNodes.tail.isEmpty) {
       reporter.reportErrorMessage(jsCall, MessageKind.WRONG_ARGUMENT_FOR_JS);
       return new NativeBehavior();
     }
 
-    var specArgument = argNodes.head;
+    dynamic specArgument = argNodes.head;
     if (specArgument is! StringNode || specArgument.isInterpolation) {
       reporter.reportErrorMessage(
           specArgument, MessageKind.WRONG_ARGUMENT_FOR_JS_FIRST);
       return new NativeBehavior();
     }
 
-    var codeArgument = argNodes.tail.head;
+    dynamic codeArgument = argNodes.tail.head;
     if (codeArgument is! StringNode || codeArgument.isInterpolation) {
       reporter.reportErrorMessage(
           codeArgument, MessageKind.WRONG_ARGUMENT_FOR_JS_SECOND);
       return new NativeBehavior();
     }
 
     String specString = specArgument.dartString.slowToString();
     String codeString = codeArgument.dartString.slowToString();
 
     return ofJsCall(
@@ skipping 501 matching lines @@
   @override
   bool get trustJSInteropTypeAnnotations =>
       compiler.options.trustJSInteropTypeAnnotations;
 
   @override
   DiagnosticReporter get reporter => compiler.reporter;
 
   @override
   Resolution get resolution => compiler.resolution;
 }