Allow scrolling a page with selection after long-press on whitespace

ui/touch_selection/touch_selection_controller.h

Index: ui/touch_selection/touch_selection_controller.h
diff --git a/ui/touch_selection/touch_selection_controller.h b/ui/touch_selection/touch_selection_controller.h
index ae0161b7734e3658f822d9a8ebc534206dcc1db6..164f2a9df8c357e15cfa37f44663dc44482ae82e 100644
--- a/ui/touch_selection/touch_selection_controller.h
+++ b/ui/touch_selection/touch_selection_controller.h
@@ -101,6 +101,10 @@ class UI_TOUCH_SELECTION_EXPORT TouchSelectionController
   bool WillHandleLongPressEvent(base::TimeTicks event_time,
                                 const gfx::PointF& location);
 
+  // To be called before forwarding a gesture scroll begin event to prevent
+  // long-press drag.
+  void OnScrollBeginEvent();
+
   // Allow showing the selection handles from the most recent selection bounds
   // update (if valid), or a future valid bounds update.
   void AllowShowingFromCurrentSelection();