Revert "Change some platform libraries to use `part of URI`."

sdk/lib/async/stream_controller.dart

 // Copyright (c) 2012, 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.
 
-part of "dart:async";
+part of dart.async;
 
 // -------------------------------------------------------------------
 // Controller for creating and adding events to a stream.
 // -------------------------------------------------------------------
 
 /**
  * Type of a stream controller's `onListen`, `onPause` and `onResume` callbacks.
  */
 typedef void ControllerCallback();
 
@@ skipping 948 matching lines @@
   var varData;
 
   _StreamControllerAddStreamState(_StreamController<T> controller, this.varData,
       Stream source, bool cancelOnError)
       : super(controller, source, cancelOnError) {
     if (controller.isPaused) {
       addSubscription.pause();
     }
   }
 }