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 0076b4ab4c9d2b2f4218a74227fcea3347d831c9..d6335f8a48e17b07fd43bd27e1b6fe3d6fdec3a6 100644
--- a/cc/scheduler/scheduler.h
+++ b/cc/scheduler/scheduler.h
@@ -16,6 +16,7 @@
 #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"
@@ -207,9 +208,9 @@ class CC_EXPORT Scheduler : public BeginFrameObserverMixIn {
   base::TimeDelta estimated_parent_draw_time_;
 
   std::deque<BeginFrameArgs> begin_retro_frame_args_;
-  BeginFrameArgs begin_impl_frame_args_;
   SchedulerStateMachine::BeginImplFrameDeadlineMode
       begin_impl_frame_deadline_mode_;
+  BeginFrameTracker begin_impl_frame_tracker_;
 
   base::Closure begin_retro_frame_closure_;
   base::Closure begin_impl_frame_deadline_closure_;
@@ -236,7 +237,7 @@ class CC_EXPORT Scheduler : public BeginFrameObserverMixIn {
   void BeginRetroFrame();
   void BeginImplFrameWithDeadline(const BeginFrameArgs& args);
   void BeginImplFrameSynchronous(const BeginFrameArgs& args);
-  void BeginImplFrame();
+  void BeginImplFrame(const BeginFrameArgs& args);
   void FinishImplFrame();
   void OnBeginImplFrameDeadline();
   void PollToAdvanceCommitState();