Avoid double task trampoline for Pipeline state transitions.

media/base/demuxer.h

 // Copyright (c) 2012 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_DEMUXER_H_
 #define MEDIA_BASE_DEMUXER_H_
 
 #include <vector>
 
 #include "base/time/time.h"
@@ skipping 40 matching lines @@
   typedef base::Callback<void(const std::string& type,
                               const std::vector<uint8>& init_data)>
       EncryptedMediaInitDataCB;
 
   Demuxer();
   ~Demuxer() override;
 
   // Completes initialization of the demuxer.
   //
   // The demuxer does not own |host| as it is guaranteed to outlive the
-  // lifetime of the demuxer. Don't delete it!
+  // lifetime of the demuxer. Don't delete it!  |status_cb| must only be run
+  // after this method has returned.
   virtual void Initialize(DemuxerHost* host,
                           const PipelineStatusCB& status_cb,
                           bool enable_text_tracks) = 0;
 
   // Carry out any actions required to seek to the given time, executing the
   // callback upon completion.
   virtual void Seek(base::TimeDelta time,
                     const PipelineStatusCB& status_cb) = 0;
 
   // Stops this demuxer.
@@ skipping 10 matching lines @@
   // a null Time is returned.
   virtual base::Time GetTimelineOffset() const = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(Demuxer);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_DEMUXER_H_