Adds BeginFrameControl via DevTools.

cc/scheduler/scheduler_state_machine.h

Index: cc/scheduler/scheduler_state_machine.h
diff --git a/cc/scheduler/scheduler_state_machine.h b/cc/scheduler/scheduler_state_machine.h
index 3d119822e0b2358324852291c7db856d35916b81..ede27d6c767c17ddcb3e930d708ebefd80d4e867 100644
--- a/cc/scheduler/scheduler_state_machine.h
+++ b/cc/scheduler/scheduler_state_machine.h
@@ -270,6 +270,9 @@ class CC_EXPORT SchedulerStateMachine {
   void SetVideoNeedsBeginFrames(bool video_needs_begin_frames);
   bool video_needs_begin_frames() const { return video_needs_begin_frames_; }
 
+  void SetBeginFrameAllowsLatencyOptimizations(
+      bool allow_latency_optimizations);
+
  protected:
   bool BeginFrameRequiredForAction() const;
   bool BeginFrameNeededForVideo() const;
@@ -283,6 +286,7 @@ class CC_EXPORT SchedulerStateMachine {
 
   bool ShouldBeginCompositorFrameSinkCreation() const;
   bool ShouldDraw() const;
+  bool ShouldForceDraw() const;
   bool ShouldActivatePendingTree() const;
   bool ShouldSendBeginMainFrame() const;
   bool ShouldCommit() const;
@@ -344,6 +348,7 @@ class CC_EXPORT SchedulerStateMachine {
   bool wait_for_ready_to_draw_;
   bool did_draw_in_last_frame_;
   bool did_submit_in_last_frame_;
+  bool begin_frame_allows_latency_optimizations_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SchedulerStateMachine);