Send a GSB to main thread before switching to it in the middle of scrolling.

ui/events/blink/input_handler_proxy_client.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_EVENTS_BLINK_INPUT_HANDLER_PROXY_CLIENT_H_
 #define UI_EVENTS_BLINK_INPUT_HANDLER_PROXY_CLIENT_H_
 
 #include "ui/events/blink/web_input_event_traits.h"
 
 namespace blink {
@@ skipping 37 matching lines @@
   virtual void DidOverscroll(
       const gfx::Vector2dF& accumulated_overscroll,
       const gfx::Vector2dF& latest_overscroll_delta,
       const gfx::Vector2dF& current_fling_velocity,
       const gfx::PointF& causal_event_viewport_point) = 0;
 
   virtual void DidStopFlinging() = 0;
 
   virtual void DidAnimateForInput() = 0;
 
+  // Used to send a GSB to the main thread when the wheel scroll latching is
+  // enabled and the scrolling should switch to the main thread.
+  virtual void GenerateScrollBeginAndSendToMainThread(
+      const blink::WebGestureEvent& update_event) = 0;
+
  protected:
   virtual ~InputHandlerProxyClient() {}
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_BLINK_INPUT_HANDLER_PROXY_CLIENT_H_