Add BeginFrameObserverProxy

ui/compositor/compositor.cc

Index: ui/compositor/compositor.cc
diff --git a/ui/compositor/compositor.cc b/ui/compositor/compositor.cc
index 6293c2c19cf6d6e2fbb2fda6a548b18226e15cfa..69d10bf438cbcb34f2a50a9157ebd617fbdd98b6 100644
--- a/ui/compositor/compositor.cc
+++ b/ui/compositor/compositor.cc
@@ -155,6 +155,8 @@ Compositor::~Compositor() {
   FOR_EACH_OBSERVER(CompositorObserver, observer_list_,
                     OnCompositingShuttingDown(this));
 
+  DCHECK(!begin_frame_observer_list_.might_have_observers());
+
   if (root_layer_)
     root_layer_->SetCompositor(NULL);
 
@@ -282,6 +284,30 @@ bool Compositor::HasAnimationObserver(
   return animation_observer_list_.HasObserver(observer);
 }
 
+void Compositor::AddBeginFrameObserver(
+    CompositorBeginFrameObserver* observer,
+    const cc::BeginFrameArgs& last_begin_frame_args_sent_to_observer) {
+  // If |last_begin_frame_args_| is still effective, send it to the new
+  // |observer| immediately.
+  if (last_begin_frame_args_sent_to_observer.frame_time !=
+      missed_begin_frame_args_.frame_time) {
+    observer->OnSendBeginFrame(missed_begin_frame_args_);
+  }
+
+  if (!begin_frame_observer_list_.might_have_observers())
+    host_->SetChildrenNeedBeginFrames(true);
+  begin_frame_observer_list_.AddObserver(observer);
+}
+
+void Compositor::RemoveBeginFrameObserver(
+    CompositorBeginFrameObserver* observer) {
+  DCHECK(begin_frame_observer_list_.HasObserver(observer));
+  begin_frame_observer_list_.RemoveObserver(observer);
+
+  if (!begin_frame_observer_list_.might_have_observers())
+    host_->SetChildrenNeedBeginFrames(false);
+}
+
 void Compositor::BeginMainFrame(const cc::BeginFrameArgs& args) {
   FOR_EACH_OBSERVER(CompositorAnimationObserver,
                     animation_observer_list_,
@@ -342,6 +368,14 @@ void Compositor::DidAbortSwapBuffers() {
                     OnCompositingAborted(this));
 }
 
+void Compositor::SendBeginFramesToChildren(const cc::BeginFrameArgs& args) {
+  FOR_EACH_OBSERVER(CompositorBeginFrameObserver,
+                    begin_frame_observer_list_,
+                    OnSendBeginFrame(args));
+  missed_begin_frame_args_ = args;
+  missed_begin_frame_args_.type = cc::BeginFrameArgs::MISSED;
+}
+
 const cc::LayerTreeDebugState& Compositor::GetLayerTreeDebugState() const {
   return host_->debug_state();
 }