cc: Add support for sending BeginFrames for video.

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 44b21adf28012b42de61ff5649204e3a34025348..f444cecc58b12c6717ace74729c9236d1cd4dc5f 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -1676,6 +1676,9 @@ void LayerTreeHostImpl::WillBeginImplFrame(const BeginFrameArgs& args) {
     // we are beginning now.
     SetNeedsRedraw();
   }
+
+  for (auto& it : video_frame_controllers_)
+    it->OnBeginFrame(args);
 }
 
 void LayerTreeHostImpl::UpdateViewportContainerSizes() {
@@ -3093,6 +3096,21 @@ void LayerTreeHostImpl::SetNeedsRedrawForScrollbarAnimation() {
   SetNeedsRedraw();
 }
 
+void LayerTreeHostImpl::AddVideoFrameController(
+    VideoFrameController* controller) {
+  bool was_empty = video_frame_controllers_.empty();
+  video_frame_controllers_.insert(controller);
+  if (was_empty)
+    client_->SetVideoNeedsBeginFrames(true);
+}
+
+void LayerTreeHostImpl::RemoveVideoFrameController(
+    VideoFrameController* controller) {
+  video_frame_controllers_.erase(controller);
+  if (video_frame_controllers_.empty())
+    client_->SetVideoNeedsBeginFrames(false);
+}
+
 void LayerTreeHostImpl::SetTreePriority(TreePriority priority) {
   if (!tile_manager_)
     return;