Delete dart_backend from compiler.

tests/compiler/dart2js/backend_dart/test_helper.dart

-// Copyright (c) 2014, 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 dart_backend.test_helper;
-
-import 'dart:async';
-import 'package:async_helper/async_helper.dart';
-import 'package:compiler/compiler.dart' as api;
-import 'package:compiler/src/compiler.dart';
-import '../../../../pkg/analyzer2dart/test/test_helper.dart';
-import '../compiler_helper.dart';
-
-/// Compiles the given dart code (which must include a 'main' function) and
-/// returns the compiler.
-Future<Compiler> compilerFor(String code,
-                             {api.CompilerOutputProvider outputProvider}) {
-  MockCompiler compiler = new MockCompiler.internal(
-      emitJavaScript: false,
-      enableMinification: false,
-      outputProvider: outputProvider);
-  compiler.diagnosticHandler = createHandler(compiler, code);
-  return compiler.init().then((_) {
-    compiler.parseScript(code);
-
-    Element element = compiler.mainApp.find('main');
-    if (element == null) return null;
-
-    compiler.mainFunction = element;
-    compiler.phase = Compiler.PHASE_RESOLVING;
-    compiler.backend.enqueueHelpers(compiler.enqueuer.resolution,
-                                    compiler.globalDependencies);
-    compiler.processQueue(compiler.enqueuer.resolution, element);
-    compiler.world.populate();
-    compiler.backend.onResolutionComplete();
-
-    compiler.irBuilder.buildNodes();
-
-    return compiler;
-  });
-}
-
-/// Test group using async_helper.
-asyncTester(Group group, RunTest runTest) {
-  asyncTest(() => Future.forEach(group.results, runTest));
-}