cc: Throttle swaps in Scheduler instead of OutputSurface

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 d6de2af1a96bb7914192e579e3b7ab3cc9a57dd7..990c13573398d9fe42930aab2f6ab9db03c3adfe 100644
--- a/cc/scheduler/scheduler_state_machine.h
+++ b/cc/scheduler/scheduler_state_machine.h
@@ -176,10 +176,21 @@ class CC_EXPORT SchedulerStateMachine {
   // ManageTiles will occur shortly (even if no redraw is required).
   void SetNeedsManageTiles();
 
+  // Sets how many swaps can be pending to the OutputSurface.
+  void SetMaxSwapsPending(int max);
+
+  // If the scheduler attempted to draw and swap, this provides feedback
+  // regarding whether or not the swap actually occured. We might skip the
+  // swap when there is not damage, for example.

[Sami, 2014/04/08 13:42:19]

Not directly related to this patch, but I always wondered why we decide to skip
drawing when there's no damage in LTHI::DrawLayers instead of in
LTHI::PrepareToDraw. It seems like it would be cleaner to have a different
DrawSwapReadbackResult for that case.

+  void DidSwapBuffers();
+
   // Indicates whether a redraw is required because we are currently rendering
   // with a low resolution or checkerboarded tile.
   void SetSwapUsedIncompleteTile(bool used_incomplete_tile);
 
+  // Notification from the OutputSurface that a swap has been consumed.
+  void OnSwapBuffersComplete();

[Sami, 2014/04/08 13:42:19]

bikeshed: DidSwapBuffersComplete to match the scheduler naming convention? Or
just keep the OutputSurface naming like you did -- up to you.

+
   // Indicates whether to prioritize animation smoothness over new content
   // activation.
   void SetSmoothnessTakesPriority(bool smoothness_takes_priority);
@@ -302,6 +313,8 @@ class CC_EXPORT SchedulerStateMachine {
   // ManageTile per BeginImplFrame.
   int manage_tiles_funnel_;
   int consecutive_checkerboard_animations_;
+  int max_pending_swaps_;
+  int pending_swaps_;
   bool needs_redraw_;
   bool needs_manage_tiles_;
   bool swap_used_incomplete_tile_;