Add helpers library to dart2js.

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

 // Copyright (c) 2011, 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.
 
 part of dart2js;
 
 const DONT_KNOW_HOW_TO_FIX = "";
 
 /**
  * The messages in this file should meet the following guide lines:
@@ skipping 1456 matching lines @@
       const MessageKind(
       "Argument for 'JS_INTERCEPTOR_CONSTANT' must be a type constant.");
 
   static const MessageKind EXPECTED_IDENTIFIER_NOT_RESERVED_WORD =
       const MessageKind(
           "'#{keyword}' is a reserved word and can't be used here.",
           howToFix: "Try using a different name.",
           examples: const ["do() {} main() {}"]);
 
   static const MessageKind UNUSED_METHOD = const MessageKind(
-      "The method '#{method_name}' is never called.",
+      "The method '#{name}' is never called.",
       howToFix: "Consider deleting it.",
       examples: const ["deadCode() {} main() {}"]);
 
+  static const MessageKind UNUSED_CLASS = const MessageKind(
+      "The class '#{name}' is never used.",
+      howToFix: "Consider deleting it.",
+      examples: const ["class DeadCode {} main() {}"]);
+
+  static const MessageKind UNUSED_TYPEDEF = const MessageKind(
+      "The typedef '#{name}' is never used.",
+      howToFix: "Consider deleting it.",
+      examples: const ["typedef DeadCode(); main() {}"]);
+
   static const MessageKind ABSTRACT_METHOD = const MessageKind(
       "The method '#{name}' has no implementation in "
       "class '#{class}'.",
       howToFix: "Try adding a body to '#{name}' or declaring "
                 "'#{class}' to be 'abstract'.",
       examples: const ["""
 class Class {
   method();
 }
 main() => new Class();
@@ skipping 432 matching lines @@
     return computeMessage();
   }
 
   bool operator==(other) {
     if (other is !Message) return false;
     return (kind == other.kind) && (toString() == other.toString());
   }
 
   int get hashCode => throw new UnsupportedError('Message.hashCode');
 }