Re-target wheel events only when a new scroll sequence has started.

content/browser/renderer_host/render_widget_host_input_event_router.h

 // Copyright 2015 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 CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_INPUT_EVENT_ROUTER_H_
 #define CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_INPUT_EVENT_ROUTER_H_
 
 #include <stdint.h>
 
 #include <deque>
@@ skipping 146 matching lines @@
   void SendGestureScrollEnd(RenderWidgetHostViewBase* view,
                             const blink::WebGestureEvent& event);
 
   FrameSinkIdOwnerMap owner_map_;
   TargetQueue touchscreen_gesture_target_queue_;
   TargetData touch_target_;
   TargetData touchscreen_gesture_target_;
   TargetData touchpad_gesture_target_;
   TargetData bubbling_gesture_scroll_target_;
   TargetData first_bubbling_scroll_target_;
+  // Used to target wheel events for the duration of a scroll when wheel scroll
+  // latching is enabled.
+  TargetData wheel_target_;
   // Maintains the same target between mouse down and mouse up.
   TargetData mouse_capture_target_;
 
   // Tracked for the purpose of generating MouseEnter and MouseLeave events.
   RenderWidgetHostViewBase* last_mouse_move_target_;
   RenderWidgetHostViewBase* last_mouse_move_root_view_;
 
   int active_touches_;
   // Keep track of when we are between GesturePinchBegin and GesturePinchEnd
   // inclusive, as we need to route these events (and anything in between) to
   // the main frame.
   bool in_touchscreen_gesture_pinch_;
   bool gesture_pinch_did_send_scroll_begin_;
   std::unordered_map<cc::SurfaceId, HittestData, cc::SurfaceIdHash>
       hittest_data_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostInputEventRouter);
   FRIEND_TEST_ALL_PREFIXES(SitePerProcessBrowserTest,
                            InputEventRouterGestureTargetQueueTest);
   FRIEND_TEST_ALL_PREFIXES(SitePerProcessBrowserTest,
                            InputEventRouterTouchpadGestureTargetTest);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_INPUT_EVENT_ROUTER_H_