Revert "Remove Compiler.assembledCode."

tests/compiler/dart2js/backend_dart/dart_backend_test.dart

 // Copyright (c) 2012, 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 'dart:async';
 import "package:async_helper/async_helper.dart";
 import '../mock_compiler.dart';
 import '../mock_libraries.dart';
-import '../output_collector.dart';
 import 'package:compiler/compiler.dart';
 import 'package:compiler/src/dart2jslib.dart' as leg;
 import 'package:compiler/src/dart_backend/dart_backend.dart';
 import 'package:compiler/src/elements/elements.dart';
 import 'package:compiler/src/tree/tree.dart';
 
 const ioLib = r'''
 library io;
 class Platform {
   static int operatingSystem;
@@ skipping 64 matching lines @@
     }
   }
 
   final options = <String>['--output-type=dart'];
   // Some tests below are using dart:io.
   options.add('--categories=Client,Server');
   if (minify) options.add('--minify');
   if (stripTypes) options.add('--force-strip=types');
 
   asyncTest(() {
-    OutputCollector outputCollector = new OutputCollector();
     return compile(
         scriptUri,
         fileUri('libraryRoot/'),
         fileUri('packageRoot/'),
         provider,
         handler,
-        options,
-        outputCollector).then((_) {
-      String code = outputCollector.getOutput('', 'dart');
-      Expect.equals(expectedResult, code,
-          'expected:\n$expectedResult\nactual:\n$code');
+        options).then((s) {
+      Expect.equals(expectedResult, s,
+          'expected:\n$expectedResult\nactual:\n$s');
     });
   });
 }
 
 testSimpleFileUnparse() {
   final src = '''
 should_be_dropped() {
 }
 
 should_be_kept() {
@@ skipping 990 matching lines @@
   testParametersMinified();
   testDeclarationTypePlaceholders();
   testPlatformLibraryMemberNamesAreFixed();
   testConflictsWithCoreLib();
   testUnresolvedNamedConstructor1();
   testUnresolvedNamedConstructor2();
   testUnresolvedNamedConstructor3();
   testClassAndNamedMixinDeclarations();
 }