gpu video: optimize HW video to SW canvas and implement it for WebRTC.

cc/resources/video_resource_updater.cc

Index: cc/resources/video_resource_updater.cc
diff --git a/cc/resources/video_resource_updater.cc b/cc/resources/video_resource_updater.cc
index 63750574a4f72ad3097e1703bf6ed8990ad2138f..0e772ebf22eccac90563463f609d3807b03989c1 100644
--- a/cc/resources/video_resource_updater.cc
+++ b/cc/resources/video_resource_updater.cc
@@ -296,7 +296,9 @@ VideoFrameExternalResources VideoResourceUpdater::CreateForSoftwarePlanes(
       ResourceProvider::ScopedWriteLockSoftware lock(
           resource_provider_, plane_resource.resource_id);
       SkCanvas canvas(lock.sk_bitmap());
-      video_renderer_->Copy(video_frame, &canvas);
+      // This is software path, so canvas and video_frame are always backed
+      // by software.
+      video_renderer_->Copy(video_frame, &canvas, media::Context3D());
       SetPlaneResourceUniqueId(video_frame.get(), 0, &plane_resource);
     }