Fix wrong type annotations.

sdk/lib/_internal/compiler/implementation/js_backend/native_emitter.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/native_emitter.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/native_emitter.dart b/sdk/lib/_internal/compiler/implementation/js_backend/native_emitter.dart
index c2f3ae5dcfa7b57d53ccc31b76fb2e25d7ecbc59..589dff0dbe6f59ba025bd505dce2366a2577a656 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/native_emitter.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/native_emitter.dart
@@ -321,12 +321,12 @@ function(cls, desc) {
     // Temporary variables for common substrings.
     List<String> varNames = <String>[];
     // var -> expression
-    Map<String, js.Expression> varDefns = <String, js.Expression>{};
+    Map<dynamic, js.Expression> varDefns = new Map<dynamic, js.Expression>();
     // tag -> expression (a string or a variable)
     Map<ClassElement, js.Expression> tagDefns =
         new Map<ClassElement, js.Expression>();
 
-    String makeExpression(ClassElement classElement) {
+    js.Expression makeExpression(ClassElement classElement) {
       // Expression fragments for this set of cls keys.
       List<js.Expression> expressions = <js.Expression>[];
       // TODO: Remove if cls is abstract.
@@ -334,7 +334,7 @@ function(cls, desc) {
       void walk(ClassElement cls) {
         for (final ClassElement subclass in getDirectSubclasses(cls)) {
           ClassElement tag = subclass;
-          String existing = tagDefns[tag];
+          var existing = tagDefns[tag];
           if (existing == null) {
             subtags.add(toNativeName(tag));
             walk(subclass);
@@ -376,7 +376,8 @@ function(cls, desc) {
     if (!tagDefns.isEmpty) {
       List<js.Statement> statements = <js.Statement>[];
 
-      List<js.Expression> initializations = <js.Expression>[];
+      List<js.VariableInitialization> initializations =
+          <js.VariableInitialization>[];
       for (final String varName in varNames) {
         initializations.add(
             new js.VariableInitialization(