Make elements/names.dart its own library

pkg/compiler/lib/src/js_backend/mirrors_analysis.dart

 // Copyright (c) 2016, 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.
 
 library dart2js.mirrors_handler;
 
 import '../common.dart';
 import '../common/resolution.dart';
 import '../compiler.dart';
 import '../constants/values.dart';
 import '../diagnostics/diagnostic_listener.dart';
 import '../elements/elements.dart';
 import '../elements/entities.dart';
+import '../elements/names.dart';
 import '../enqueue.dart';
 import '../universe/selector.dart';
 import '../universe/use.dart';
 import '../universe/world_impact.dart';
 import 'backend.dart';
 import 'constant_handler_javascript.dart';
 import 'mirrors_data.dart';
 
 abstract class MirrorsResolutionAnalysis {
   void onQueueEmpty(Enqueuer enqueuer, Iterable<ClassEntity> recentClasses);
@@ skipping 451 matching lines @@
 
 /// Records that [constant] is used by the element behind [registry].
 class Dependency {
   final ConstantValue constant;
   final Element annotatedElement;
 
   const Dependency(this.constant, this.annotatedElement);
 
   String toString() => '$annotatedElement:${constant.toStructuredText()}';
 }