Make elements/names.dart its own library

tests/compiler/dart2js/serialization/members_test.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.serialization.class_members_test;
 
 import 'dart:async';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/common/names.dart';
 import 'package:compiler/src/commandline_options.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/elements/elements.dart';
+import 'package:compiler/src/elements/names.dart';
 import 'package:compiler/src/filenames.dart';
 import 'package:compiler/src/resolution/class_members.dart';
 import 'package:compiler/src/serialization/equivalence.dart';
 import '../memory_compiler.dart';
 import 'helper.dart';
 import 'test_helper.dart';
 
 main(List<String> args) {
   Arguments arguments = new Arguments.from(args);
   asyncTest(() async {
@@ skipping 116 matching lines @@
       areTypesEquivalent);
   check(class1, class2, '$property.functionType', member1.functionType,
       member2.functionType, areTypesEquivalent);
   check(
       class1, class2, '$property.isGetter', member1.isGetter, member2.isGetter);
   check(
       class1, class2, '$property.isSetter', member1.isSetter, member2.isSetter);
   check(
       class1, class2, '$property.isMethod', member1.isMethod, member2.isMethod);
 }