Avoid double task trampoline for Pipeline state transitions.

media/base/renderer.h

 // 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.
 
 #ifndef MEDIA_BASE_RENDERER_H_
 #define MEDIA_BASE_RENDERER_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/time/time.h"
@@ skipping 12 matching lines @@
   typedef base::Callback<void(const scoped_refptr<VideoFrame>&)> PaintCB;
   typedef base::Callback<base::TimeDelta()> TimeDeltaCB;
 
   Renderer();
 
   // Stops rendering and fires any pending callbacks.
   virtual ~Renderer();
 
   // Initializes the Renderer with |demuxer_stream_provider|, executing
   // |init_cb| upon completion.  If initialization failed, fires |error_cb|
-  // before |init_cb|. |demuxer_stream_provider| must be valid throughout the
-  // lifetime of the Renderer object.
+  // before |init_cb|.  |demuxer_stream_provider| must be valid throughout the
+  // lifetime of the Renderer object.  |init_cb| must only be run after this
+  // method has returned.
   //
   // Permanent callbacks:
   // - |statistics_cb|: Executed periodically with rendering statistics.
   // - |buffering_state_cb|: Executed when buffering state is changed.
   // - |paint_cb|: Executed when there is a VideoFrame ready to paint.  Can be
   //               ignored if the Renderer handles the painting by itself. Can
   //               be called from any thread.
   // - |ended_cb|: Executed when rendering has reached the end of stream.
   // - |error_cb|: Executed if any error was encountered during rendering.
   virtual void Initialize(DemuxerStreamProvider* demuxer_stream_provider,
@@ skipping 32 matching lines @@
   // Returns whether |this| renders video.
   virtual bool HasVideo() = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(Renderer);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_RENDERER_H_