Add support for external video renderers in mojo.

media/mojo/interfaces/media_renderer.mojom

 // Copyright 2014 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.
 
 module mojo;
 
 import "media/mojo/interfaces/demuxer_stream.mojom";
 import "media/mojo/interfaces/media_types.mojom";
 
 [Client=MediaRendererClient]
 interface MediaRenderer {
-  // Initializes the Renderer with |stream|, calling back upon completion.
+  // Initializes the Renderer with one or both of an audio and video stream,
+  // calling back upon completion.
   // NOTE: If an error occurs, MediaRendererClient::OnError() will be called
   // before the callback is executed.
-  Initialize(DemuxerStream stream) => ();
+  Initialize(DemuxerStream? audio, DemuxerStream? video) => ();
 
   // Discards any buffered data, executing callback when completed.
   // NOTE: If an error occurs, MediaRendererClient::OnError() can be called
   // before the callback is executed.
   Flush() => ();
 
   // Starts rendering from |time_usec|.
   StartPlayingFrom(int64 time_usec);
 
   // Updates the current playback rate. The default playback rate should be 1.
@@ skipping 16 matching lines @@
   OnBufferingStateChange(BufferingState state);
 
   // Executed when rendering has reached the end of stream.
   OnEnded();
 
   // Executed if any error was encountered during decode or rendering. If
   // this error happens during an operation that has a completion callback,
   // OnError() will be called before firing the completion callback.
   OnError();
 };