Don't require VDAs to return all PictureBuffers at once.

media/filters/gpu_video_decoder.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_FILTERS_GPU_VIDEO_DECODER_H_
 #define MEDIA_FILTERS_GPU_VIDEO_DECODER_H_
 
 #include <list>
 #include <map>
 #include <set>
@@ skipping 117 matching lines @@
   // Request a shared-memory segment of at least |min_size| bytes.  Will
   // allocate as necessary.
   scoped_ptr<SHMBuffer> GetSHM(size_t min_size);
 
   // Return a shared-memory segment to the available pool.
   void PutSHM(scoped_ptr<SHMBuffer> shm_buffer);
 
   // Destroy all PictureBuffers in |buffers|, and delete their textures.
   void DestroyPictureBuffers(PictureBufferMap* buffers);
 
-  // Returns true if the video decoder can support |profile| and |coded_size|.
-  bool IsProfileSupported(VideoCodecProfile profile,
-                          const gfx::Size& coded_size);
+  // Returns true if the video decoder with |capabilities| can support
+  // |profile| and |coded_size|.
+  bool IsProfileSupported(
+      const VideoDecodeAccelerator::Capabilities& capabilities,
+      VideoCodecProfile profile,
+      const gfx::Size& coded_size);
 
   // Assert the contract that this class is operated on the right thread.
   void DCheckGpuVideoAcceleratorFactoriesTaskRunnerIsCurrent() const;
 
   bool needs_bitstream_conversion_;
 
   GpuVideoAcceleratorFactories* factories_;
 
   // Populated during Initialize() (on success) and unchanged until an error
   // occurs.
@@ skipping 45 matching lines @@
 
   // picture_buffer_id and the frame wrapping the corresponding Picture, for
   // frames that have been decoded but haven't been requested by a Decode() yet.
   int32 next_picture_buffer_id_;
   int32 next_bitstream_buffer_id_;
 
   // Set during ProvidePictureBuffers(), used for checking and implementing
   // HasAvailableOutputFrames().
   int available_pictures_;
 
+  // If false, then we may assume that the VDA cannot stall sending picture
+  // buffers until all of them have decoded frames.  If true, then it may
+  // stall as long as one picture buffer is outstanding.

[Pawel Osciak, 2015/12/05 00:18:55]

Please clarify what "outstanding" means, where the buffer is, what is its state
(decoded/empty/etc.), etc.

[liberato (no reviews please), 2015/12/07 19:04:39]

done.  please let me know if the new text is more clear.

+  bool can_stall_anytime_;

[Pawel Osciak, 2015/12/05 00:18:55]

What does "anytime" mean? Should we drop it? It's also confusing, since I
believe if can_stall_anytime_ == true and buffers are not allocated, then it
won't stall actually?

[liberato (no reviews please), 2015/12/07 19:04:39]

true, which is why i tried to frame it as "one picture buffer outstanding" in
the docs.  i agree with the sentiment, but couldn't find a shorter name for it. 
suggestions are welcome.

+
   // Bound to factories_->GetMessageLoop().
   // NOTE: Weak pointers must be invalidated before all other member variables.
   base::WeakPtrFactory<GpuVideoDecoder> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(GpuVideoDecoder);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_FILTERS_GPU_VIDEO_DECODER_H_