cc: Don't attempt main thread synchronization if it is slow.

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 e6a7222e1a368e7dcf0230e022aa9de5c22a7d6b..5028fe64d4887aa7b9113cef83100159f1cd3bb0 100644
--- a/cc/scheduler/scheduler_state_machine.h
+++ b/cc/scheduler/scheduler_state_machine.h
@@ -193,10 +193,14 @@ class CC_EXPORT SchedulerStateMachine {
 
   // Indicates whether to prioritize impl thread latency (i.e., animation
   // smoothness) over new content activation.
-  void SetImplLatencyTakesPriority(bool impl_latency_takes_priority);
-  bool impl_latency_takes_priority() const {
-    return impl_latency_takes_priority_;
-  }
+  void SetSmoothnessMode(bool smoothness_takes_priority,
+                         bool scroll_affects_scroll_handler);
+
+  // Indicates if the main thread will likely respond within 1 vsync.
+  void SetMainThreadIsFast(bool is_fast);
+
+  // A function of SetSmoothnessMode and SetMainThreadIsFast.
+  bool ImplLatencyTakesPriority() const;
 
   // Indicates whether ACTION_DRAW_AND_SWAP_IF_POSSIBLE drew to the screen.
   void DidDrawIfPossibleCompleted(DrawResult result);
@@ -328,7 +332,9 @@ class CC_EXPORT SchedulerStateMachine {
   bool pending_tree_is_ready_for_activation_;
   bool active_tree_needs_first_draw_;
   bool did_create_and_initialize_first_output_surface_;
-  bool impl_latency_takes_priority_;
+  bool smoothness_takes_priority_;
+  bool scroll_affects_scroll_handler_;
+  bool main_thread_is_fast_;
   bool main_thread_missed_last_deadline_;
   bool skip_next_begin_main_frame_to_reduce_latency_;
   bool children_need_begin_frames_;