cc: Introduce forward_begin_frames_to_children and use_external_begin_frame_source

cc/trees/layer_tree_settings.h

Index: cc/trees/layer_tree_settings.h
diff --git a/cc/trees/layer_tree_settings.h b/cc/trees/layer_tree_settings.h
index 74a3b0c85bbe942c2150fbee97a490d6ab79e97a..775797e0ef509802a6967feea3239ddb98a7d3b8 100644
--- a/cc/trees/layer_tree_settings.h
+++ b/cc/trees/layer_tree_settings.h
@@ -23,7 +23,8 @@ class CC_EXPORT LayerTreeSettings {
   bool force_antialiasing;
   bool throttle_frame_production;
   bool single_thread_proxy_scheduler;
-  bool begin_frame_scheduling_enabled;
+  bool begin_frame_receiver;
+  bool begin_frame_publisher;
   bool main_frame_before_activation_enabled;
   bool using_synchronous_renderer_compositor;
   bool disable_hi_res_timer_tasks_on_battery;