cc: Adding BeginFrameTracker object and removing Now() from LTHI.

cc/scheduler/scheduler.h

Index: cc/scheduler/scheduler.h
diff --git a/cc/scheduler/scheduler.h b/cc/scheduler/scheduler.h
index dea7c3e541004fd0bce31f182b501ca0e16be845..2b49ea63c33110d160759b8eb7cc573adb14946f 100644
--- a/cc/scheduler/scheduler.h
+++ b/cc/scheduler/scheduler.h
@@ -18,6 +18,7 @@
 #include "cc/output/begin_frame_args.h"
 #include "cc/output/vsync_parameter_observer.h"
 #include "cc/scheduler/begin_frame_source.h"
+#include "cc/scheduler/begin_frame_tracker.h"
 #include "cc/scheduler/delay_based_time_source.h"
 #include "cc/scheduler/draw_result.h"
 #include "cc/scheduler/scheduler_settings.h"
@@ -202,9 +203,9 @@ class CC_EXPORT Scheduler : public BeginFrameObserverMixIn,
 
   bool begin_retro_frame_posted_;
   std::deque<BeginFrameArgs> begin_retro_frame_args_;
-  BeginFrameArgs begin_impl_frame_args_;
   SchedulerStateMachine::BeginImplFrameDeadlineMode
       begin_impl_frame_deadline_mode_;
+  BeginFrameTracker begin_impl_frame_args_;
 
   base::Closure begin_retro_frame_closure_;
   base::Closure begin_unthrottled_frame_closure_;