Move video encode accelerator IPC messages to GPU IO thread

media/gpu/media_foundation_video_encode_accelerator_win.h

Index: media/gpu/media_foundation_video_encode_accelerator_win.h
diff --git a/media/gpu/media_foundation_video_encode_accelerator_win.h b/media/gpu/media_foundation_video_encode_accelerator_win.h
index 3060abb194cdedaa5900e5e63c78e331d8f51ccb..08dcd4d843f014cfd8bf41ef55e700489ebc16e2 100644
--- a/media/gpu/media_foundation_video_encode_accelerator_win.h
+++ b/media/gpu/media_foundation_video_encode_accelerator_win.h
@@ -28,10 +28,11 @@ namespace media {
 // Media Foundation implementation of the VideoEncodeAccelerator interface for
 // Windows.
 // This class saves the task runner on which it is constructed and returns
-// encoded data to the client using that same task runner. This class has
-// DCHECKs to makes sure that methods are called in sequence. It starts an
-// internal encoder thread on which VideoEncodeAccelerator implementation tasks
-// are posted.
+// encoded data to the client using that same task runner. If
+// TryToSetupEncodeOnSeparateThread() is called, it uses the given
+// |encode_task_runner| instead. This class has DCHECKs to makes sure that
+// methods are called in sequence. It starts an internal encoder thread on which
+// VideoEncodeAccelerator implementation tasks are posted.
 class MEDIA_GPU_EXPORT MediaFoundationVideoEncodeAccelerator
     : public VideoEncodeAccelerator {
  public:
@@ -50,6 +51,10 @@ class MEDIA_GPU_EXPORT MediaFoundationVideoEncodeAccelerator
   void RequestEncodingParametersChange(uint32_t bitrate,
                                        uint32_t framerate) override;
   void Destroy() override;
+  bool TryToSetupEncodeOnSeparateThread(
+      const base::WeakPtr<Client>& encode_client,
+      const scoped_refptr<base::SingleThreadTaskRunner>& encode_task_runner)
+      override;
 
   // Preload dlls required for encoding.
   static void PreSandboxInitialization();
@@ -130,9 +135,15 @@ class MEDIA_GPU_EXPORT MediaFoundationVideoEncodeAccelerator
   std::unique_ptr<base::WeakPtrFactory<Client>> client_ptr_factory_;
 
   // Our original calling task runner for the child thread.
-  const scoped_refptr<base::SequencedTaskRunner> client_task_runner_;
-  // Sequence checker to enforce that the methods of this object are called in
-  // sequence.
+  scoped_refptr<base::SequencedTaskRunner> client_task_runner_;
+
+  // Thread checker to enforce that this object created, initialized and
+  // destroyed on a specific thread. It is pinned on the thread where object is
+  // created.
+  base::ThreadChecker thread_checker_;
+
+  // Sequence checker to enforce that the encode tasks of this object are called
+  // in sequence.
   base::SequenceChecker sequence_checker_;
 
   // This thread services tasks posted from the VEA API entry points by the