Emit to StreamCodeOutput instead of CodeBuffer.

tests/try/poi/apply_updates_test.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.
 
 // Test of FunctionUpdate by pretty printing the updated element before and
 // after.
 library trydart.library_updater_test;
 
 import 'package:dart2js_incremental/library_updater.dart' show
     IncrementalCompilerContext,
     LibraryUpdater,
     Update;
 
 import 'package:compiler/src/scanner/scannerlib.dart' show
     PartialFunctionElement;
 
 import 'package:compiler/src/dart2jslib.dart' show
     Script;
 
-import 'package:compiler/src/source_file.dart' show
+import 'package:compiler/src/io/source_file.dart' show
     StringSourceFile;
 
 import 'compiler_test_case.dart';
 
 import 'library_updater_test.dart' show
     LibraryUpdaterTestCase,
     newScriptFrom,
     nolog;
 
 class ApplyUpdateTestCase extends LibraryUpdaterTestCase {
@@ skipping 67 matching lines @@
 
           new ApplyUpdateTestCase(
               before: 'main(){}',
               after: 'main()=>null;',
               update: 'main'),
 
           // TODO(ahe): When supporting class members, test abstract methods.
       ]
   );
 }