Make RendererGpuVideoDecoderFactories live on arbitrary threads.

content/renderer/media/media_stream_dependency_factory.cc

Index: content/renderer/media/media_stream_dependency_factory.cc
diff --git a/content/renderer/media/media_stream_dependency_factory.cc b/content/renderer/media/media_stream_dependency_factory.cc
index f15f1036fbd1830f86fdd17e2544e55cc306aff6..890d2d7badacd9666bfd8686ec10b845c2c570a2 100644
--- a/content/renderer/media/media_stream_dependency_factory.cc
+++ b/content/renderer/media/media_stream_dependency_factory.cc
@@ -497,10 +497,17 @@ bool MediaStreamDependencyFactory::CreatePeerConnectionFactory() {
 
     const CommandLine* cmd_line = CommandLine::ForCurrentProcess();
     if (cmd_line->HasSwitch(switches::kEnableWebRtcHWDecoding)) {
-      scoped_refptr<media::GpuVideoDecoder::Factories> gpu_factories =
-          RenderThreadImpl::current()->GetGpuFactories();
-      if (gpu_factories.get() != NULL)
-        decoder_factory.reset(new RTCVideoDecoderFactory(gpu_factories));
+      scoped_ptr<base::Thread> vda_thread(new base::Thread("vda_thread"));

[scherkus (not reviewing), 2013/07/18 00:54:43]

OOC what warrants using a separate thread? Is it your comment about the
libjingle worker thread being pegged?

Is it possible to use some other existing thread? (e.g., render thread, IO,
media thread, some other process-wide thread...)

If not, can we make this a lazily-allocated process-wide thread?

[wuchengli, 2013/07/18 09:42:00]

libjingle worker thread being pegged only means I cannot use it in
RtcVideoDecoder and RGVDF.

Using media thread sounds like a good idea. What RtcVideoDecoder does is similar
to GpuVideoDecoder. It makes them more consistent. I've changed the code to use
media thread.

By the way, I verified that the performance of using libjingle worker thread is
worse than using media thread or a new thread.

+      bool started = vda_thread->Start();
+      scoped_refptr<content::RendererGpuVideoDecoderFactories> gpu_factories;
+      if (started) {
+        gpu_factories = RenderThreadImpl::current()->GetGpuFactories(
+            vda_thread->message_loop_proxy());
+      }
+      if (gpu_factories.get() != NULL) {
+        decoder_factory.reset(
+            new RTCVideoDecoderFactory(vda_thread.Pass(), gpu_factories));
+      }
     }
 #if defined(GOOGLE_TV)
     // PeerConnectionFactory will hold the ownership of this