Make elements/names.dart its own library

tests/compiler/dart2js/needs_no_such_method_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.
 
 import 'dart:async';
 import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'package:compiler/src/common.dart';
-import 'package:compiler/src/elements/elements.dart'
-    show Element, ClassElement, PublicName;
+import 'package:compiler/src/elements/elements.dart' show ClassElement;
+import 'package:compiler/src/elements/names.dart';
 import 'package:compiler/src/universe/call_structure.dart';
 import 'package:compiler/src/universe/selector.dart';
 import 'package:compiler/src/world.dart' show ClosedWorld, ClassQuery;
 import 'type_test_helper.dart';
 
 void main() {
   asyncTest(() async {
     await testClassSets();
   });
 }
@@ skipping 260 matching lines @@
   check(subtype, ClassQuery.EXACT, foo, true);
   check(subtype, ClassQuery.EXACT, bar, false);
   check(subtype, ClassQuery.EXACT, baz, true);
   check(subtype, ClassQuery.SUBCLASS, foo, true);
   check(subtype, ClassQuery.SUBCLASS, bar, false);
   check(subtype, ClassQuery.SUBCLASS, baz, true);
   check(subtype, ClassQuery.SUBTYPE, foo, true);
   check(subtype, ClassQuery.SUBTYPE, bar, false);
   check(subtype, ClassQuery.SUBTYPE, baz, true);
 }