Add renames in output when using the mirror helper library.

tests/compiler/dart2js/mirror_helper_unique_minification_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.
 
 import "package:expect/expect.dart";
 import 'memory_compiler.dart' show compilerFor;
 import '../../../sdk/lib/_internal/compiler/implementation/apiimpl.dart' show
     Compiler;
 import
     '../../../sdk/lib/_internal/compiler/implementation/dart_backend/dart_backend.dart'
@@ skipping 15 matching lines @@
   backend.useMirrorHelperLibrary = useMirrorHelperLibrary;
   compiler.runCompiler(Uri.parse('memory:main.dart'));
   return compiler;
 }
 
 void testUniqueMinification() {
   Compiler compiler = runCompiler(useMirrorHelperLibrary: true, minify: true);
   DartBackend backend = compiler.backend;
   Map<Node, String> renames = backend.renames;
 
-  //'Foo' appears twice, so toSet() reduces the length by 1.
-  Expect.equals(renames.values.toSet().length, renames.values.length - 1);
+  //'Foo' appears twice, so toSet() reduces the length by 1,
+  // and the extra code from mirror_helper.dart adds 9 duplicates.
+  Expect.equals(renames.values.toSet().length, renames.values.length - 10);
 }
 
 void testNoUniqueMinification() {
   Compiler compiler = runCompiler(useMirrorHelperLibrary: false, minify: true);
   DartBackend backend = compiler.backend;
   Map<Node, String> renames = backend.renames;
 
   //'Foo' appears twice and now 'invocation' and 'hest' can get the same name.
   Expect.equals(renames.values.toSet().length, renames.values.length - 2);
 }
 
 const MEMORY_SOURCE_FILES = const <String, String> {
   'main.dart': """
 import 'dart:mirrors';
 
 class Foo {
   noSuchMethod(invocation) {
     MirrorSystem.getName(const Symbol('hest'));
   }
 }
 
 main() {
   new Foo().fisk();
   var hest;
 }
 """};