Create a new action triggered when a BeginMainFrame is not expected before vsync

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 cd4a7f2ee6689c969354e511fad775a8980d3355..20fe3f1441e629dafab349fac14986778f0bc896 100644
--- a/cc/scheduler/scheduler_state_machine.h
+++ b/cc/scheduler/scheduler_state_machine.h
@@ -123,6 +123,7 @@ class CC_EXPORT SchedulerStateMachine {
     ACTION_BEGIN_COMPOSITOR_FRAME_SINK_CREATION,
     ACTION_PREPARE_TILES,
     ACTION_INVALIDATE_COMPOSITOR_FRAME_SINK,
+    ACTION_DO_SHORT_IDLE_WORK,

[Sami, 2017/03/30 15:30:36]

ACTION_NOTIFY_BEGIN_MAIN_FRAME_NOT_SENT

[Dan Elphick, 2017/04/06 16:10:17]

Done.

   };
   static const char* ActionToString(Action action);
 
@@ -131,6 +132,7 @@ class CC_EXPORT SchedulerStateMachine {
 
   Action NextAction() const;
   void WillSendBeginMainFrame();
+  void WillDoShortIdleWork();
   void WillCommit(bool commit_had_no_updates);
   void WillActivate();
   void WillDraw();
@@ -318,6 +320,7 @@ class CC_EXPORT SchedulerStateMachine {
   bool ShouldCommit() const;
   bool ShouldPrepareTiles() const;
   bool ShouldInvalidateCompositorFrameSink() const;
+  bool ShouldDoShortIdleWork() const;
 
   void WillDrawInternal();
   void WillPerformImplSideInvalidationInternal();
@@ -356,9 +359,10 @@ class CC_EXPORT SchedulerStateMachine {
   // These are used to ensure that an action only happens once per frame,
   // deadline, etc.
   bool draw_funnel_;
-  bool send_begin_main_frame_funnel_;
+  bool did_send_begin_main_frame_for_current_frame_;
   bool invalidate_compositor_frame_sink_funnel_;
   bool impl_side_invalidation_funnel_;
+  bool did_do_idle_work_;

[Sami, 2017/03/30 15:30:37]

Let's also add a flag saying whether we did a commit in this frame and avoid
idling in that case.

[Dan Elphick, 2017/04/06 16:10:16]

Done.

   // prepare_tiles_funnel_ is "filled" each time PrepareTiles is called
   // and "drained" on each BeginImplFrame. If the funnel gets too full,
   // we start throttling ACTION_PREPARE_TILES such that we average one