Call VideoFrameProviderImpl::DidReceiveFrame when background render completes.

media/blink/video_frame_compositor.cc

Index: media/blink/video_frame_compositor.cc
diff --git a/media/blink/video_frame_compositor.cc b/media/blink/video_frame_compositor.cc
index 3cdf980ba0aa6136f9729e8925cc4518c665d9f7..3e3d62bc21eb227717c475f722d9f786f9dab096 100644
--- a/media/blink/video_frame_compositor.cc
+++ b/media/blink/video_frame_compositor.cc
@@ -219,7 +219,9 @@ void VideoFrameCompositor::BackgroundRender() {
   DCHECK(compositor_task_runner_->BelongsToCurrentThread());
   const base::TimeTicks now = tick_clock_->NowTicks();
   last_background_render_ = now;
-  CallRender(now, now + last_interval_, true);
+  bool new_frame = CallRender(now, now + last_interval_, true);
+  if (new_frame && client_)
+    client_->DidReceiveFrame();

[DaleCurtis, 2015/08/14 21:50:03]

Hmm, this means we're calling SetNeedsRedraw() even for occluded/invisible
frames -- which seemed wasteful and thus wasn't done here. Is that concern moot?
It is every 250ms, so I think it might be. 

[DaleCurtis, 2015/08/14 21:51:41]

Actually this can happen as frequently as every 4ms when slaved to WebGL.  See
http://ro.me/ where this might happen.

 }
 
 bool VideoFrameCompositor::CallRender(base::TimeTicks deadline_min,