Add helpers library to dart2js.

sdk/lib/_internal/compiler/implementation/elements/elements.dart

Index: sdk/lib/_internal/compiler/implementation/elements/elements.dart
diff --git a/sdk/lib/_internal/compiler/implementation/elements/elements.dart b/sdk/lib/_internal/compiler/implementation/elements/elements.dart
index d9bc5d6fa7b34fd81793d458cc11226b52e9061e..2e5dd423421e4c1cabac929dbe333cc4bc89d8aa 100644
--- a/sdk/lib/_internal/compiler/implementation/elements/elements.dart
+++ b/sdk/lib/_internal/compiler/implementation/elements/elements.dart
@@ -761,8 +761,6 @@ abstract class TypedefElement extends Element
   FunctionSignature get functionSignature;
   Link<DartType> get typeVariables;
 
-  bool get isResolved;
-
   // TODO(kasperl): Try to get rid of these setters.
   void set alias(DartType value);
   void set functionSignature(FunctionSignature value);
@@ -872,6 +870,8 @@ abstract class TypeDeclarationElement extends Element {
    * [computeType].
    */
   Link<DartType> get typeVariables;
+
+  bool get isResolved;
 }
 
 abstract class ClassElement extends TypeDeclarationElement
@@ -901,7 +901,6 @@ abstract class ClassElement extends TypeDeclarationElement
 
   int get supertypeLoadState;
   int get resolutionState;
-  bool get isResolved;
   String get nativeTagInfo;
 
   bool get isMixinApplication;