Move video encode accelerator IPC messages to GPU IO thread

media/video/video_encode_accelerator.h

Index: media/video/video_encode_accelerator.h
diff --git a/media/video/video_encode_accelerator.h b/media/video/video_encode_accelerator.h
index ac1ffd56dfa8a1f51a54c5e7d7284a7584c174fc..2d10da73982f025f1f218a055fb2c4cb622e9c64 100644
--- a/media/video/video_encode_accelerator.h
+++ b/media/video/video_encode_accelerator.h
@@ -12,6 +12,8 @@
 #include <vector>
 
 #include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
+#include "base/single_thread_task_runner.h"
 #include "media/base/bitstream_buffer.h"
 #include "media/base/media_export.h"
 #include "media/base/video_decoder_config.h"
@@ -147,11 +149,29 @@ class MEDIA_EXPORT VideoEncodeAccelerator {
 
   // Destroys the encoder: all pending inputs and outputs are dropped
   // immediately and the component is freed.  This call may asynchronously free
-  // system resources, but its client-visible effects are synchronous.  After
-  // this method returns no more callbacks will be made on the client.  Deletes
+  // system resources, but its client-visible effects are synchronous. After
+  // this method returns no more callbacks will be made on the client. Deletes
   // |this| unconditionally, so make sure to drop all pointers to it!
   virtual void Destroy() = 0;
 
+  // Encode tasks include these methods that are used frequently during the
+  // session: Encode(), UseOutputBitstreamBuffer(),
+  // RequestEncodingParametersChange(), Client::BitstreamBufferReady().
+  // If the Client can support running these on a separate thread, it may
+  // call this method to try to set up the VEA implementation to do so.
+  //
+  // If the VEA can support this as well, return true, otherwise return false.
+  // If true is returned, the client may submit each of these calls on
+  // |encode_task_runner|, and then expect Client::BitstreamBufferReady() to be
+  // called on |encode_task_runner| as well; called on |encode_client|, instead
+  // of |client| provided to Initialize().
+  //
+  // One application of this is offloading the GPU main thread. This helps
+  // reduce latency and jitter by avoiding the wait.
+  virtual bool TryToSetupEncodeOnSeparateThread(
+      const base::WeakPtr<Client>& encode_client,
+      const scoped_refptr<base::SingleThreadTaskRunner>& encode_task_runner);
+
  protected:
   // Do not delete directly; use Destroy() or own it with a scoped_ptr, which
   // will Destroy() it properly by default.