Remove warnings from dart2js test-suite.

tests/compiler/dart2js/mirrors_used_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.
 
 /// Test that the @MirrorsUsed annotation suppress hints and that only
 /// requested elements are retained for reflection.
 library dart2js.test.mirrors_used_test;
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
 
 import 'memory_compiler.dart' show
     compilerFor;
 
 import '../../../sdk/lib/_internal/compiler/implementation/apiimpl.dart' show
     Compiler;
 
 import '../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart' show
     Constant,
     TypeConstant;
 
 import
     '../../../sdk/lib/_internal/compiler/implementation/elements/elements.dart'
-show
-    Elements;
+show Element, Elements;
+import '../../../sdk/lib/_internal/compiler/implementation/js_backend/js_backend.dart'
+    show JavaScriptBackend;
 
 void expectOnlyVerboseInfo(Uri uri, int begin, int end, String message, kind) {
   if (kind.name == 'verbose info') {
     print(message);
     return;
   }
   if (message.contains('methods retained for use by dart:mirrors out of')) {
     print(message);
     return;
   }
@@ skipping 38 matching lines @@
     [
         'Foo_staticMethod', // The name of Foo.staticMethod.
         r'instanceMethod$0']; // The name of Foo.instanceMethod.
 
     // We always include the names of some native classes.
     List<Element> nativeClasses = [
           compiler.intClass, compiler.doubleClass, compiler.numClass,
           compiler.stringClass, compiler.boolClass, compiler.nullClass,
           compiler.listClass
         ];
-
+    JavaScriptBackend backend = compiler.backend;
     Iterable<String> nativeNames =
-        nativeClasses.map(compiler.backend.namer.getNameOfClass);
+        nativeClasses.map(backend.namer.getNameOfClass);
     expectedNames.addAll(nativeNames);
 
     Set recordedNames = new Set()
-        ..addAll(compiler.backend.emitter.recordedMangledNames)
-        ..addAll(compiler.backend.emitter.mangledFieldNames.keys)
-        ..addAll(compiler.backend.emitter.mangledGlobalFieldNames.keys);
+        ..addAll(backend.emitter.recordedMangledNames)
+        ..addAll(backend.emitter.mangledFieldNames.keys)
+        ..addAll(backend.emitter.mangledGlobalFieldNames.keys);
     Expect.setEquals(new Set.from(expectedNames), recordedNames);
 
     for (var library in compiler.libraries.values) {
       library.forEachLocalMember((member) {
         if (library == compiler.mainApp && member.name == 'Foo') {
           Expect.isTrue(
               compiler.backend.isNeededForReflection(member), '$member');
           member.forEachLocalMember((classMember) {
             Expect.isTrue(
                 compiler.backend.isNeededForReflection(classMember),
                 '$classMember');
           });
         } else {
           Expect.isFalse(
               compiler.backend.isNeededForReflection(member), '$member');
         }
       });
     }
 
     // There should at least be one metadata constant:
     // 1. The constructed constant for 'MirrorsUsed'.
-    Expect.isTrue(compiler.backend.metadataConstants.length >= 1);
+    Expect.isTrue(backend.metadataConstants.length >= 1);
 
-    Set<Constant> compiledConstants =
-        compiler.backend.constants.compiledConstants;
+    Set<Constant> compiledConstants = backend.constants.compiledConstants;
     // Make sure that most of the metadata constants aren't included in the
     // generated code.
-    for (var dependency in compiler.backend.metadataConstants) {
+    for (var dependency in backend.metadataConstants) {
       Constant constant = dependency.constant;
       Expect.isFalse(compiledConstants.contains(constant), '$constant');
     }
 
     // The type literal 'Foo' is both used as metadata, and as a plain value in
     // the program. Make sure that it isn't duplicated.
     int fooConstantCount = 0;
     for (Constant constant in compiledConstants) {
       if (constant is TypeConstant && '${constant.representedType}' == 'Foo') {
         fooConstantCount++;
@@ skipping 31 matching lines @@
 library lib;
 
 import 'dart:mirrors';
 
 useReflect(type) {
   print(new Symbol('Foo'));
   print(MirrorSystem.getName(reflectClass(type).owner.qualifiedName));
 }
 """,
 };