Create and test source mapping for invocations.

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 CloningEventSink implements EventSink<String> {
+  final List<EventSink<String>> sinks;
+
+  CloningEventSink(this.sinks);
+
+  @override
+  void add(String event) {
+    sinks.forEach((EventSink<String> sink) => sink.add(event));
+  }
+
+  @override
+  void addError(errorEvent, [StackTrace stackTrace]) {
+    sinks.forEach((EventSink<String> sink) {
+      sink.addError(errorEvent, stackTrace);
+    });
+  }
+
+  @override
+  void close() {
+    sinks.forEach((EventSink<String> sink) => sink.close());
+  }
+}
+
 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;
   }
 }