Make new StreamController be async by default.

sdk/lib/_internal/compiler/implementation/dart2js.dart

 // Copyright (c) 2013, 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.
 
 library dart2js.cmdline;
 
 import 'dart:async';
 import 'dart:collection' show Queue, LinkedHashMap;
 import 'dart:io';
 import 'dart:utf';
@@ skipping 304 matching lines @@
         String sourceMapTag = '//@ sourceMappingURL=$sourceMapFileName\n';
         sink.count += sourceMapTag.length;
         output.write(sourceMapTag);
       }
       output.close();
       if (isPrimaryOutput) {
         charactersWritten += sink.count;
       }
     }
 
-    var controller = new StreamController<String>();
+    var controller = new StreamController<String>(sync: true);
     controller.stream.listen(output.write, onDone: onDone);
     sink = new CountingSink(controller);
     return sink;
   }
 
   api.compile(uri, libraryRoot, packageRoot,
               inputProvider.readStringFromUri, handler,
               options, outputProvider)
       .then(compilationDone);
 }
@@ skipping 179 matching lines @@
       print(trace);
     } finally {
       exit(253); // 253 is recognized as a crash by our test scripts.
     }
   }
 }
 
 void main() {
   mainWithErrorHandler(new Options());
 }