V4L2SVDA: Move allocation from GPU Child thread to decoder thread.

Allocation may take time, and we don't need to be on the GPU Child
thread to do it. This also removes the explicit synchronization between
the decoder and GPU Child threads during picture set change.

BUG=574241
TEST=vdatest,crosvideo.appspot

Review URL: https://codereview.chromium.org/1643123003

Cr-Commit-Position: refs/heads/master@{#376120}

content/common/gpu/media/v4l2_slice_video_decode_accelerator.h

@@ -155,21 +155,21 @@ class CONTENT_EXPORT V4L2SliceVideoDecodeAccelerator
 
   // Dismiss all |picture_buffer_ids| via Client::DismissPictureBuffer()
   // and signal |done| after finishing.
-  void DismissPictures(std::vector<int32_t> picture_buffer_ids,
+  void DismissPictures(const std::vector<int32_t>& picture_buffer_ids,
                        base::WaitableEvent* done);
 
   // Task to finish initialization on decoder_thread_.
   void InitializeTask();
 
   // Surface set change (resolution change) flow.
-  // If we have no surfaces allocated, just allocate them and return.
-  // Otherwise mark us as pending for surface set change.
+  // If we have no surfaces allocated, start it immediately, otherwise mark
+  // ourselves as pending for surface set change.
   void InitiateSurfaceSetChange();
   // If a surface set change is pending and we are ready, stop the device,
   // destroy outputs, releasing resources and dismissing pictures as required,
-  // followed by allocating a new set for the new resolution/DPB size
-  // as provided by decoder. Finally, try to resume decoding.
-  void FinishSurfaceSetChangeIfNeeded();
+  // followed by starting the flow to allocate a new set for the current
+  // resolution/DPB size, as provided by decoder.
+  bool FinishSurfaceSetChange();
 
   void NotifyError(Error error);
   void DestroyTask();
@@ -187,20 +187,41 @@ class CONTENT_EXPORT V4L2SliceVideoDecodeAccelerator
   // Tell the decoder to flush all frames, reset it and mark us as scheduled
   // for flush, so that we can finish it once all pending decodes are finished.
   void InitiateFlush();
-  // If all pending frames are decoded and we are waiting to flush, perform it.
-  // This will send all pending pictures to client and notify the client that
-  // flush is complete and puts us in a state ready to resume.
-  void FinishFlushIfNeeded();
+  // To be called if decoder_flushing_ is true. If not all pending frames are
+  // decoded, return false, requesting the caller to try again later.
+  // Otherwise perform flush by sending all pending pictures to the client,
+  // notify it that flush is finished and return true, informing the caller
+  // that further progress can be made.
+  bool FinishFlush();
 
   // Reset flow when requested by client.
-  // Drop all inputs and reset the decoder and mark us as pending for reset.
+  // Drop all inputs, reset the decoder and mark us as pending for reset.
   void ResetTask();
-  // If all pending frames are decoded and we are waiting to reset, perform it.
-  // This drops all pending outputs (client is not interested anymore),
-  // notifies the client we are done and puts us in a state ready to resume.
-  void FinishResetIfNeeded();
-
-  // Process pending events if any.
+  // To be called if decoder_resetting_ is true. If not all pending frames are
+  // decoded, return false, requesting the caller to try again later.
+  // Otherwise perform reset by dropping all pending outputs (client is not
+  // interested anymore), notifying it that reset is finished, and return true,
+  // informing the caller that further progress can be made.
+  bool FinishReset();
+
+  // Allocate V4L2 buffers and assign them to |buffers| provided by the client
+  // via AssignPictureBuffers() on decoder thread.
+  void AssignPictureBuffersTask(
+    const std::vector<media::PictureBuffer>& buffers);
+
+  // Create EGLImages bound to textures in |buffers| for given
+  // |output_format_fourcc| and |output_planes_count|.
+  void CreateEGLImages(const std::vector<media::PictureBuffer>& buffers,
+                       uint32_t output_format_fourcc,
+                       size_t output_planes_count);
+
+  // Assign |egl_images| to previously-allocated V4L2 buffers in
+  // output_buffer_map_ and picture ids from |buffers| and finish the surface
+  // change sequence.
+  void AssignEGLImages(const std::vector<media::PictureBuffer>& buffers,
+                       const std::vector<EGLImageKHR>& egl_images);
+
+  // Process pending events, if any.
   void ProcessPendingEventsIfNeeded();
 
   // Performed on decoder_thread_ as a consequence of poll() on decoder_thread_
@@ -377,10 +398,6 @@ class CONTENT_EXPORT V4L2SliceVideoDecodeAccelerator
   // The number of pictures that are sent to PictureReady and will be cleared.
   int picture_clearing_count_;
 
-  // Used by the decoder thread to wait for AssignPictureBuffers to arrive
-  // to avoid races with potential Reset requests.
-  base::WaitableEvent pictures_assigned_;
-
   // Make the GL context current callback.
   base::Callback<bool(void)> make_context_current_;