Notify Blink about start of gesture scroll through a queued event.

content/browser/renderer_host/input/input_router_impl.cc

Index: content/browser/renderer_host/input/input_router_impl.cc
diff --git a/content/browser/renderer_host/input/input_router_impl.cc b/content/browser/renderer_host/input/input_router_impl.cc
index 4f020675f6c9dede08ec957b15b5cd726d461bf5..9a39bf8945f75f4d1f827be61d8f9eace80db9d6 100644
--- a/content/browser/renderer_host/input/input_router_impl.cc
+++ b/content/browser/renderer_host/input/input_router_impl.cc
@@ -158,8 +158,11 @@ void InputRouterImpl::SendGestureEvent(
 
   wheel_event_queue_.OnGestureScrollEvent(gesture_event);
 
-  if (gesture_event.event.sourceDevice == blink::WebGestureDeviceTouchscreen)
+  if (gesture_event.event.sourceDevice == blink::WebGestureDeviceTouchscreen) {
+    if (gesture_event.event.type == blink::WebInputEvent::GestureScrollBegin)
+      touch_event_queue_.PrependTouchScrollNotification();
     touch_event_queue_.OnGestureScrollEvent(gesture_event);
+  }
 
   gesture_event_queue_.QueueEvent(gesture_event);
 }