[media] Support parent thread decode in VdaVideoDecoder.

Bug: 522298
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: I48b205e7b20cf512e953d5992be6ed507add688b
Reviewed-on: https://chromium-review.googlesource.com/1217716Reviewed-by: Frank Liberato <liberato@chromium.org>
Commit-Queue: Dan Sanders <sandersd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590479}

media/gpu/ipc/service/vda_video_decoder.cc

@@ -318,11 +318,13 @@ void VdaVideoDecoder::InitializeOnGpuThread() {
     return;
   }
 
-  // TODO(sandersd): TryToSetupDecodeOnSeparateThread().
   gpu_weak_vda_factory_.reset(
       new base::WeakPtrFactory<VideoDecodeAccelerator>(vda_.get()));
   gpu_weak_vda_ = gpu_weak_vda_factory_->GetWeakPtr();
+
   vda_initialized_ = true;
+  decode_on_parent_thread_ = vda_->TryToSetupDecodeOnSeparateThread(
+      parent_weak_this_, parent_task_runner_);
 
   parent_task_runner_->PostTask(FROM_HERE,
                                 base::BindOnce(&VdaVideoDecoder::InitializeDone,
@@ -374,6 +376,11 @@ void VdaVideoDecoder::Decode(scoped_refptr<DecoderBuffer> buffer,
   timestamps_.Put(bitstream_buffer_id, buffer->timestamp());
   decode_cbs_[bitstream_buffer_id] = decode_cb;
 
+  if (decode_on_parent_thread_) {
+    vda_->Decode(std::move(buffer), bitstream_buffer_id);
+    return;
+  }
+
   gpu_task_runner_->PostTask(
       FROM_HERE,
       base::BindOnce(&VdaVideoDecoder::DecodeOnGpuThread, gpu_weak_this_,

media/gpu/ipc/service/vda_video_decoder.h

@@ -187,16 +187,17 @@ class VdaVideoDecoder : public VideoDecoder,
   // large enough to account for any amount of frame reordering.
   base::MRUCache<int32_t, base::TimeDelta> timestamps_;
 
-  //
-  // GPU thread state.
-  //
-  std::unique_ptr<VideoDecodeAccelerator> vda_;
-  bool vda_initialized_ = false;
-
   //
   // Shared state.
   //
+  // Only read on GPU thread during initialization, which is mutually exclusive
+  // with writes on the parent thread.
   VideoDecoderConfig config_;
+  // Only written on the GPU thread during initialization, which is mutually
+  // exclusive with reads on the parent thread.
+  std::unique_ptr<VideoDecodeAccelerator> vda_;
+  bool vda_initialized_ = false;
+  bool decode_on_parent_thread_ = false;
 
   //
   // Weak pointers, prefixed by bound thread.