Make RendererGpuVideoDecoderFactories live on arbitrary threads.

content/renderer/media/rtc_video_decoder.h

Index: content/renderer/media/rtc_video_decoder.h
diff --git a/content/renderer/media/rtc_video_decoder.h b/content/renderer/media/rtc_video_decoder.h
index fc95ccb039e5cd758c25c31c68f9b5548c098aba..3d1538628307b5d707825f5e30796eb64c3e0e2f 100644
--- a/content/renderer/media/rtc_video_decoder.h
+++ b/content/renderer/media/rtc_video_decoder.h
@@ -35,13 +35,11 @@ class DecoderBuffer;
 namespace content {
 
 // This class uses hardware accelerated video decoder to decode video for
-// WebRTC. The message loop of RendererGpuVideoDecoderFactories is stored as
-// |vda_message_loop_|. It is the compositor thread, or the renderer thread if
-// threaded compositing is disabled. VDA::Client methods run on
-// |vda_message_loop_|. webrtc::VideoDecoder methods run on WebRTC
+// WebRTC. |vda_message_loop_| is the message loop proxy of the media thread,
+// which VDA::Client methods run on. webrtc::VideoDecoder methods run on WebRTC
 // DecodingThread or Chrome_libJingle_WorkerThread, which are trampolined to
 // |vda_message_loop_|. Decode() is non-blocking and queues the buffers. Decoded
-// frames are delivered on |vda_message_loop_|.
+// frames are delivered to WebRTC on |vda_message_loop_|.
 class CONTENT_EXPORT RTCVideoDecoder
     : NON_EXPORTED_BASE(public webrtc::VideoDecoder),
       public media::VideoDecodeAccelerator::Client,
@@ -49,8 +47,10 @@ class CONTENT_EXPORT RTCVideoDecoder
  public:
   virtual ~RTCVideoDecoder();
 
-  // Creates a RTCVideoDecoder. Returns NULL if failed.
+  // Creates a RTCVideoDecoder. Returns NULL if failed. The video decoder will
+  // run on the message loop of |factories|.
   static scoped_ptr<RTCVideoDecoder> Create(
+      webrtc::VideoCodecType type,
       const scoped_refptr<media::GpuVideoDecoder::Factories>& factories);
 
   // webrtc::VideoDecoder implementation.
@@ -110,6 +110,7 @@ class CONTENT_EXPORT RTCVideoDecoder
 
   FRIEND_TEST_ALL_PREFIXES(RTCVideoDecoderTest, IsBufferAfterReset);
 
+  // The meessage loop of |factories| will be saved to |vda_loop_proxy_|.
   RTCVideoDecoder(
       const scoped_refptr<media::GpuVideoDecoder::Factories>& factories);
 
@@ -197,19 +198,9 @@ class CONTENT_EXPORT RTCVideoDecoder
 
   scoped_refptr<media::GpuVideoDecoder::Factories> factories_;
 
-  // The message loop to run callbacks on. This is should be the same as the one
-  // of |factories_|.
+  // The message loop to run callbacks on. This is from |factories_|.
   scoped_refptr<base::MessageLoopProxy> vda_loop_proxy_;
 
-  // The thread to create shared memory. Factories::CreateSharedMemory is
-  // trampolined to the child thread. When |vda_loop_proxy_| is the compositor
-  // thread, blocking on the child thread will deadlock. During WebRTC hang up,
-  // the child thread waits for Chrome_libJingle_WorkerThread. libJingle thread
-  // cannot finish when DecodingThread holds a WebRTC lock and blocks on the
-  // child thread. So we need to call CreateSharedMemory asynchronously from a
-  // different thread.
-  base::Thread create_shm_thread_;
-
   // The texture target used for decoded pictures.
   uint32 decoder_texture_target_;