Allow Preroll() call on VideoRendererImpl without a Flush().

media/base/video_renderer.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_VIDEO_RENDERER_H_
 #define MEDIA_BASE_VIDEO_RENDERER_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/time/time.h"
@@ skipping 56 matching lines @@
   // |callback| when playback is underway.
   virtual void Play(const base::Closure& callback) = 0;
 
   // Temporarily suspend decoding and rendering video, executing |callback| when
   // playback has been suspended.
   virtual void Pause(const base::Closure& callback) = 0;
 
   // Discard any video data, executing |callback| when completed.
   virtual void Flush(const base::Closure& callback) = 0;
 
-  // Start prerolling video data for samples starting at |time|, executing
-  // |callback| when completed.
+  // Start prerolling video data. If |time| equals kNoTimestamp() then all
+  // samples delivered to the renderer are used to complete preroll. If |time|
+  // does not equal kNoTimestamp(), then any samples delivered to the renderer
+  // with timestamps less than |time| are silently dropped and not used to
+  // satisfy preroll. |callback| is executed when preroll has completed.
   //
-  // Only valid to call after a successful Initialize() or Flush().
+  // Only valid to call after a successful Initialize(), Pause(), or Flush().
   virtual void Preroll(base::TimeDelta time,
                        const PipelineStatusCB& callback) = 0;
 
   // Stop all operations in preparation for being deleted, executing |callback|
   // when complete.
   virtual void Stop(const base::Closure& callback) = 0;
 
   // Updates the current playback rate.
   virtual void SetPlaybackRate(float playback_rate) = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(VideoRenderer);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_VIDEO_RENDERER_H_