dart2js: Use an abstract Name class for names in the generated JavaScript ast.

tests/compiler/dart2js/mirrors_used_test.dart

 // Copyright (c) 2013, 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.
 
 /// Test that the @MirrorsUsed annotation suppress hints and that only
 /// requested elements are retained for reflection.
 library dart2js.test.mirrors_used_test;
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
@@ skipping 68 matching lines @@
         r'instanceMethod$0']; // The name of Foo.instanceMethod.
 
     // We always include the names of some native classes.
     List<Element> nativeClasses = [
           compiler.intClass, compiler.doubleClass, compiler.numClass,
           compiler.stringClass, compiler.boolClass, compiler.nullClass,
           compiler.listClass
         ];
     JavaScriptBackend backend = compiler.backend;
     Iterable<String> nativeNames = nativeClasses.map(backend.namer.className);
+    expectedNames = expectedNames.map(backend.namer.asName).toList();
     expectedNames.addAll(nativeNames);
 
     Set recordedNames = new Set()
         ..addAll(backend.emitter.oldEmitter.recordedMangledNames)
         ..addAll(backend.emitter.oldEmitter.mangledFieldNames.keys)
         ..addAll(backend.emitter.oldEmitter.mangledGlobalFieldNames.keys);
     Expect.setEquals(new Set.from(expectedNames), recordedNames);
 
     for (var library in compiler.libraryLoader.libraries) {
       library.forEachLocalMember((member) {
@@ skipping 66 matching lines @@
 library lib;
 
 import 'dart:mirrors';
 
 useReflect(type) {
   print(new Symbol('Foo'));
   print(MirrorSystem.getName(reflectClass(type).owner.qualifiedName));
 }
 """,
 };