Revert "Remove Compiler.assembledCode."

tests/compiler/dart2js/output_collector.dart

-// Copyright (c) 2015, 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.
-
-// Output provider that collects the output in string buffers.
-
-library output_collector;
-
-import 'dart:async';
-
-class BufferedEventSink implements EventSink<String> {
-  StringBuffer sb = new StringBuffer();
-  String text;
-
-  void add(String event) {
-    sb.write(event);
-  }
-
-  void addError(errorEvent, [StackTrace stackTrace]) {
-    // Do not support this.
-  }
-
-  void close() {
-    text = sb.toString();
-    sb = null;
-  }
-}
-
-class OutputCollector {
-  Map<String, Map<String, BufferedEventSink>> outputMap = {};
-
-  EventSink<String> call(String name, String extension) {
-    Map<String, BufferedEventSink> sinkMap =
-        outputMap.putIfAbsent(extension, () => {});
-    return sinkMap.putIfAbsent(name, () => new BufferedEventSink());
-  }
-
-  String getOutput(String name, String extension) {
-    Map<String, BufferedEventSink> sinkMap = outputMap[extension];
-    if (sinkMap == null) return null;
-    BufferedEventSink sink = sinkMap[name];
-    return sink != null ? sink.text : null;
-  }
-}