Refactor CompilerOutput

tests/compiler/dart2js/line_column_provider_test.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.
 
 // Unittest for the [LineColumnCollector].
 
 import 'package:expect/expect.dart';
 import 'package:compiler/src/io/code_output.dart';
 import 'package:compiler/src/io/line_column_provider.dart';
 
 import 'output_collector.dart';
 
 test(List events, Map<int, List<int>> expectedPositions) {
-  BufferedEventSink sink = new BufferedEventSink();
+  BufferedOutputSink sink = new BufferedOutputSink();
   LineColumnProvider lineColumnProvider = new LineColumnCollector();
   CodeOutput output = new StreamCodeOutput(sink, [lineColumnProvider]);
   for (var event in events) {
     if (event is String) {
       output.add(event);
     } else if (event is CodeBuffer) {
       output.addBuffer(event);
     }
   }
   output.close();
@@ skipping 75 matching lines @@
   test(["a", buffer2], positions);
 
   CodeBuffer buffer3 = new CodeBuffer();
   buffer3.add("a");
   test([buffer3, buffer2], positions);
 
   CodeBuffer buffer4 = new CodeBuffer();
   buffer4.addBuffer(buffer3);
   test([buffer4, buffer2], positions);
 }