Run VDA::Decode on GPU IO thread if VDA supports it.

content/common/gpu/media/vaapi_video_decode_accelerator.h

Index: content/common/gpu/media/vaapi_video_decode_accelerator.h
diff --git a/content/common/gpu/media/vaapi_video_decode_accelerator.h b/content/common/gpu/media/vaapi_video_decode_accelerator.h
index 9ac73da353e7952ec588b4d20f0b5d46c702d54e..6d2bac1a7fb080f2e043e4cd9365ae6a87047333 100644
--- a/content/common/gpu/media/vaapi_video_decode_accelerator.h
+++ b/content/common/gpu/media/vaapi_video_decode_accelerator.h
@@ -46,7 +46,8 @@ class CONTENT_EXPORT VaapiVideoDecodeAccelerator :
   VaapiVideoDecodeAccelerator(
       Display* x_display, GLXContext glx_context,
       Client* client,
-      const base::Callback<bool(void)>& make_context_current);
+      const base::Callback<bool(void)>& make_context_current,
+      const scoped_refptr<base::MessageLoopProxy>& io_message_loop);
   virtual ~VaapiVideoDecodeAccelerator();
 
   // media::VideoDecodeAccelerator implementation.
@@ -229,6 +230,9 @@ private:
   // ChildThread's message loop
   base::MessageLoop* message_loop_;
 
+  // IO message loop proxy
+  scoped_refptr<base::MessageLoopProxy> io_message_loop_;
+
   // WeakPtr<> pointing to |this| for use in posting tasks from the decoder
   // thread back to the ChildThread.  Because the decoder thread is a member of
   // this class, any task running on the decoder thread is guaranteed that this