Refactoring the way begin frame sources inside scheduler work.

cc/trees/thread_proxy.cc

Index: cc/trees/thread_proxy.cc
diff --git a/cc/trees/thread_proxy.cc b/cc/trees/thread_proxy.cc
index 19cf3ba62b9cc004bd77ca81aa4afb110b54bdf0..913281ef5f20e988cbc781a7e637859861da9132 100644
--- a/cc/trees/thread_proxy.cc
+++ b/cc/trees/thread_proxy.cc
@@ -425,7 +425,7 @@ void ThreadProxy::DidSwapBuffersCompleteOnImplThread() {
 
 void ThreadProxy::SetNeedsBeginFrame(bool enable) {
   TRACE_EVENT1("cc", "ThreadProxy::SetNeedsBeginFrame", "enable", enable);
-  impl().layer_tree_host_impl->SetNeedsBeginFrame(enable);
+  impl().scheduler.SetNeedsBeginFrame(enable);
   UpdateBackgroundAnimateTicking();
 }
 
@@ -1461,7 +1461,8 @@ void ThreadProxy::LayerTreeHostClosedOnImplThread(CompletionEvent* completion) {
   layer_tree_host()->DeleteContentsTexturesOnImplThread(
       impl().layer_tree_host_impl->resource_provider());
   impl().current_resource_update_controller.reset();
-  impl().layer_tree_host_impl->SetNeedsBeginFrame(false);
+  // impl().scheduler.
+  impl().scheduler.SetNeedsBeginFrame(false);
   impl().scheduler.reset();
   impl().layer_tree_host_impl.reset();
   impl().weak_factory.InvalidateWeakPtrs();