MouseWheelEventQueue should respect ScrollBegin/End state from RenderWidgetHost.

content/browser/renderer_host/input/input_router_client.h

Index: content/browser/renderer_host/input/input_router_client.h
diff --git a/content/browser/renderer_host/input/input_router_client.h b/content/browser/renderer_host/input/input_router_client.h
index 0221533738205bce9c75dabe055cdb781266cdb7..adffb8b8f369979bbd98fba6292095ca92c41c48 100644
--- a/content/browser/renderer_host/input/input_router_client.h
+++ b/content/browser/renderer_host/input/input_router_client.h
@@ -60,6 +60,10 @@ class CONTENT_EXPORT InputRouterClient {
   virtual void ForwardGestureEventWithLatencyInfo(
       const blink::WebGestureEvent& gesture_event,
       const ui::LatencyInfo& latency_info) = 0;
+
+  // Call this function to determine if it's necessary to insert
+  // GestureScrollBegin/Ends.
+  virtual bool IsInGestureScroll(blink::WebGestureDevice device) const = 0;
 };
 
 } // namespace content