Remove reliance on VideoToolbox frame ordering.

content/common/gpu/media/vt_video_decode_accelerator.h

Index: content/common/gpu/media/vt_video_decode_accelerator.h
diff --git a/content/common/gpu/media/vt_video_decode_accelerator.h b/content/common/gpu/media/vt_video_decode_accelerator.h
index 327ab590e2b74d134d94ac61862a5596dea2c49d..efd76df5b6a5c402e9bfeefb1dd553a9415a2ffe 100644
--- a/content/common/gpu/media/vt_video_decode_accelerator.h
+++ b/content/common/gpu/media/vt_video_decode_accelerator.h
@@ -173,9 +173,9 @@ class VTVideoDecodeAccelerator : public media::VideoDecodeAccelerator {
   // Size of assigned picture buffers.
   gfx::Size picture_size_;
 
-  // Queue of frames that have not yet been decoded; maintains ownership of the
-  // Frame objects while they flow through VideoToolbox.
-  std::queue<linked_ptr<Frame>> pending_frames_;
+  // Frames that have not yet been decoded; maintains ownership of Frame objects
+  // while they flow through VideoToolbox.
+  std::map<Frame*, linked_ptr<Frame>> pending_frames_;

[DaleCurtis, 2014/11/22 00:10:51]

Why not just an std::set?

[sandersd (OOO until July 31), 2014/11/22 00:20:40]

The linked_ptr is keeping the object alive in this situation, but I need to be
able to find that ownership by raw pointer.

(Reworking this ownership model again is planned, but probably comes after
initial rollout, testing, and bugs.)

[DaleCurtis, 2014/11/22 00:25:06]

This is really nasty though. Are you really saving yourself any work by not just
having a set<Frame*> and transferring ownership into a scoper inside the task?

[sandersd (OOO until July 31), 2014/11/22 00:32:48]

No, but inside the task I'd have to have this same structure, because I need to
be able to save the reference while the frame is owned by VideoToolbox.

As per the discussion in the work queue CL, that's no so bad if I trust
VideoToolbox to return every frame, as we can just release the ownership
instead, but Pawel didn't want to go for that option, so for now I'm changing as
little code as possible. (It's not too late though, if it's really important we
can get this done properly right away.)

[DaleCurtis, 2014/11/22 00:53:40]

I don't follow why you'd change the tasks... they already contain a linked_ptr,
so you really just need the raw ptr set between Decode and DecodeDone... At
destruction / stop / whatever you can nuke incomplete frames.

[sandersd (OOO until July 31), 2014/11/22 00:55:50]

Sorry, that's DecodeTask().

[DaleCurtis, 2014/11/25 21:56:20]

I still don't follow your arguments against set<Frame*> or
set<linked_ptr<Frame*>> here; note: you can set a custom comparator on the set.
A map of Frame* to linked_ptr<Frame> is such a strong code smell that I'm not
convinced there's not a better way here. If those Cls are still in flight they
should be changed.

 
   // Set of assigned bitstream IDs, so that Destroy() can release them all.
   std::set<int32_t> assigned_bitstream_ids_;