Make elements/names.dart its own library

tests/compiler/dart2js/lookup_member_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.
 
 library lookup_member_test;
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
 import 'type_test_helper.dart';
 import 'package:compiler/src/elements/resolution_types.dart';
 import "package:compiler/src/elements/elements.dart"
-    show Element, ClassElement, MemberSignature, PublicName;
+    show ClassElement, MemberSignature;
+import "package:compiler/src/elements/names.dart";
 
 void main() {
   test();
 }
 
 void test() {
   asyncTest(() => TypeEnvironment.create(r"""
       class A<T> {
         T foo;
       }
@@ skipping 46 matching lines @@
         expect(C_U, 'baz', U);
         expect(C_U, 'boz', instantiate(B, [U]));
 
         ResolutionDartType C_int = instantiate(C, [int_]);
         expect(C_int, 'foo', instantiate(A, [String_]));
         expect(C_int, 'bar', String_);
         expect(C_int, 'baz', int_);
         expect(C_int, 'boz', instantiate(B, [int_]));
       }));
 }