cc: Allow the main thread to cancel commits

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 325ac1cd35a264a392ef802fb491fac0932135b6..9789f3a1f6ef3642a70c2fc1e5c923d0f19d3eca 100644
--- a/cc/scheduler/scheduler_state_machine.h
+++ b/cc/scheduler/scheduler_state_machine.h
@@ -79,7 +79,7 @@ class CC_EXPORT SchedulerStateMachine {
 
   // Indicates that the system has entered and left a BeginFrame callback.
   // The scheduler will not draw more than once in a given BeginFrame
-  // callback.
+  // callback nor send more than one BeginFrame message.
   void DidEnterBeginFrame(const BeginFrameArgs& args);
   void DidLeaveBeginFrame();
   bool inside_begin_frame() const { return inside_begin_frame_; }
@@ -120,8 +120,9 @@ class CC_EXPORT SchedulerStateMachine {
 
   // Call this only in response to receiving an
   // ACTION_SEND_BEGIN_FRAME_TO_MAIN_THREAD from NextAction if the client
-  // rejects the begin frame message.
-  void BeginFrameAbortedByMainThread();
+  // rejects the begin frame message.  If did_handle is false, then
+  // another commit will be retried soon.
+  void BeginFrameAbortedByMainThread(bool did_handle);
 
   // Request exclusive access to the textures that back single buffered
   // layers on behalf of the main thread. Upon acquisition,
@@ -175,6 +176,7 @@ class CC_EXPORT SchedulerStateMachine {
   int commit_count_;
 
   int current_frame_number_;
+  int last_frame_number_where_begin_frame_sent_to_main_thread_;
   int last_frame_number_where_draw_was_called_;
   int last_frame_number_where_tree_activation_attempted_;
   int last_frame_number_where_check_for_completed_tile_uploads_called_;