Revert "Use relative URIs for core library part-of statements."

sdk/lib/async/stream_impl.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 "async.dart";
+part of dart.async;
 
 /** Abstract and private interface for a place to put events. */
 abstract class _EventSink<T> {
   void _add(T data);
   void _addError(Object error, StackTrace stackTrace);
   void _close();
 }
 
 /**
  * Abstract and private interface for a place to send events.
@@ skipping 1026 matching lines @@
 
 /** An empty broadcast stream, sending a done event as soon as possible. */
 class _EmptyStream<T> extends Stream<T> {
   const _EmptyStream() : super._internal();
   bool get isBroadcast => true;
   StreamSubscription<T> listen(void onData(T data),
       {Function onError, void onDone(), bool cancelOnError}) {
     return new _DoneStreamSubscription<T>(onDone);
   }
 }