Async Wheel Event with only the first one cancellable behind a flag.

content/browser/renderer_host/input/mouse_wheel_event_queue.h

Index: content/browser/renderer_host/input/mouse_wheel_event_queue.h
diff --git a/content/browser/renderer_host/input/mouse_wheel_event_queue.h b/content/browser/renderer_host/input/mouse_wheel_event_queue.h
index d4e9c7e97d47bdae55ee764217e55e8e0e714426..b0389f9531367d2646d01e7ffe9040cdd44447bb 100644
--- a/content/browser/renderer_host/input/mouse_wheel_event_queue.h
+++ b/content/browser/renderer_host/input/mouse_wheel_event_queue.h
@@ -90,9 +90,17 @@ class CONTENT_EXPORT MouseWheelEventQueue {
   // GSB has been sent in the past.
   bool needs_scroll_end_;
 
-  // True if the touchpad and wheel scroll latching is enabled.
+  // True if the touchpad and wheel scroll latching flag is enabled.
   bool enable_scroll_latching_;
 
+  // True if the async wheel events flag is enabled.
+  bool enable_async_wheel_events_;
+
+  // True if the ack for the first wheel event in a scroll sequence is not
+  // consumed. This lets us to send the rest of the wheel events in the sequence
+  // as non-blocking.
+  bool send_wheel_events_async_;
+
   blink::WebGestureDevice scrolling_device_;
 
   DISALLOW_COPY_AND_ASSIGN(MouseWheelEventQueue);