cc: Add main frame timing info to frame timing tracker.

cc/trees/layer_tree_host_impl.h

Index: cc/trees/layer_tree_host_impl.h
diff --git a/cc/trees/layer_tree_host_impl.h b/cc/trees/layer_tree_host_impl.h
index 2efe2dab6196301fe3cad01b49ba2ac36950010b..2c9c2048cc1d5594476c9f5a4ba6029dc8de4c7c 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -524,6 +524,19 @@ class CC_EXPORT LayerTreeHostImpl
     return frame_timing_tracker_.get();
   }
 
+  // Record main frame timing information.
+  // |start_of_main_frame_args| is the BeginFrameArgs of the beginning of the
+  // main frame (ie the frame that kicked off the main frame).
+  // |expected_next_main_frame_args| is the BeginFrameArgs of the frame that
+  // follows the completion of the main frame (whether it is activation or some
+  // other completion, such as early out). Note that if there is a main frame
+  // scheduled in that frame, then this BeginFrameArgs will become the main
+  // frame args. However, if no such frame is scheduled, then this _would_ be
+  // the main frame args if it was scheduled.
+  void RecordMainFrameTiming(
+      const BeginFrameArgs& start_of_main_frame_args,
+      const BeginFrameArgs& expected_next_main_frame_args);
+
  protected:
   LayerTreeHostImpl(
       const LayerTreeSettings& settings,