Change MediaFilter::Stop() to accept a callback so that Stop() is asynchronous.

media/base/filters.h

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Filters are connected in a strongly typed manner, with downstream filters
 // always reading data from upstream filters.  Upstream filters have no clue
 // who is actually reading from them, and return the results via callbacks.
 //
 //                         DemuxerStream(Video) <- VideoDecoder <- VideoRenderer
 // DataSource <- Demuxer <
@@ skipping 90 matching lines @@
   // The pipeline has paused playback.  Filters should fulfill any existing read
   // requests and then idle.  Filters may implement this method if they need to
   // respond to this call.
   virtual void Pause(FilterCallback* callback) {
     if (callback) {
       callback->Run();
       delete callback;
     }
   }
 
+  // TODO(boliu): Remove once Stop() is asynchronous in subclasses.
+  virtual void Stop() {}
+
   // The pipeline is being stopped either as a result of an error or because
   // the client called Stop().
-  virtual void Stop() = 0;
+  // TODO(boliu): No implementation in subclasses yet.
+  virtual void Stop(FilterCallback* callback) {
+    // TODO(boliu): Call the synchronous version for now. Remove once
+    // all filters have asynchronous stop.
+    Stop();
+
+    if (callback) {
+      callback->Run();
+      delete callback;
+    }
+  }
 
   // The pipeline playback rate has been changed.  Filters may implement this
   // method if they need to respond to this call.
   virtual void SetPlaybackRate(float playback_rate) {}
 
   // Carry out any actions required to seek to the given time, executing the
   // callback upon completion.
   virtual void Seek(base::TimeDelta time, FilterCallback* callback) {
     scoped_ptr<FilterCallback> seek_callback(callback);
     if (seek_callback.get()) {
@@ skipping 238 matching lines @@
   // buffer.
   virtual bool HasEnded() = 0;
 
   // Sets the output volume.
   virtual void SetVolume(float volume) = 0;
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_FILTERS_H_