Re-landing "UMA metrics for fractions of wheel and touch scrolls blocked on the main thread."

ui/events/blink/input_handler_proxy.h

Index: ui/events/blink/input_handler_proxy.h
diff --git a/ui/events/blink/input_handler_proxy.h b/ui/events/blink/input_handler_proxy.h
index 09b44d0cffcc53f5e23bc75158cd3fc7ebd28eea..0d3f9c122d6eaca13c9fd18680745ba0a41347b9 100644
--- a/ui/events/blink/input_handler_proxy.h
+++ b/ui/events/blink/input_handler_proxy.h
@@ -118,6 +118,8 @@ class InputHandlerProxy
  protected:
   void RecordMainThreadScrollingReasons(blink::WebGestureDevice device,
                                         uint32_t reasons);
+  void RecordScrollingThreadStatus(blink::WebGestureDevice device,
+                                   uint32_t reasons);
 
  private:
   friend class test::InputHandlerProxyTest;
@@ -245,6 +247,10 @@ class InputHandlerProxy
   // passive events not to block scrolling.
   int32_t touch_start_result_;
 
+  // The result of the last mouse wheel event. This value is used to determine
+  // whether the next wheel scroll is blocked on the Main thread or not.
+  int32_t mouse_wheel_result_;
+
   base::TimeTicks last_fling_animate_time_;
 
   // Used to record overscroll notifications while an event is being