Revert to zero-initializing buffers for FFmpegVideoDecoder

media/base/video_frame_pool.h

 // Copyright 2013 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_FRAME_POOL_H_
 #define MEDIA_BASE_VIDEO_FRAME_POOL_H_
 
 #include "media/base/media_export.h"
 #include "media/base/video_frame.h"
 
 namespace media {
 
 // Simple VideoFrame pool used to avoid unnecessarily allocating and destroying
 // VideoFrame objects. The pool manages the memory for the VideoFrame
 // returned by CreateFrame(). When one of these VideoFrames is destroyed,
 // the memory is returned to the pool for use by a subsequent CreateFrame()
 // call. The memory in the pool is retained for the life of the
 // VideoFramePool object. If the parameters passed to CreateFrame() change
 // during the life of this object, then the memory used by frames with the old
 // parameter values will be purged from the pool.
 class MEDIA_EXPORT VideoFramePool {
  public:
   VideoFramePool();
   ~VideoFramePool();
 
   // Returns a frame from the pool that matches the specified
   // parameters or creates a new frame if no suitable frame exists in
-  // the pool.
+  // the pool. The pool is drained if no matching frame is found.
+  // The buffer for the new frame will be zero initialized.  Reused frames will
+  // not be zero initialized.
   scoped_refptr<VideoFrame> CreateFrame(VideoPixelFormat format,
                                         const gfx::Size& coded_size,
                                         const gfx::Rect& visible_rect,
                                         const gfx::Size& natural_size,
                                         base::TimeDelta timestamp);
 
 protected:
   friend class VideoFramePoolTest;
 
   // Returns the number of frames in the pool for testing purposes.
   size_t GetPoolSizeForTesting() const;
 
  private:
   class PoolImpl;
   scoped_refptr<PoolImpl> pool_;
 
   DISALLOW_COPY_AND_ASSIGN(VideoFramePool);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_VIDEO_FRAME_POOL_H_