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

ui/touch_selection/touch_selection_controller.h

 // Copyright 2014 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_TOUCH_SELECTION_TOUCH_SELECTION_CONTROLLER_H_
 #define UI_TOUCH_SELECTION_TOUCH_SELECTION_CONTROLLER_H_
 
 #include "base/time/time.h"
 #include "ui/base/touch/selection_bound.h"
 #include "ui/gfx/geometry/point_f.h"
@@ skipping 83 matching lines @@
   // showing the insertion handle from subsequent bounds changes.
   // |tap_count| is tap index in a repeated sequence, i.e., 1 for the first
   // tap, 2 for the second tap, etc...
   bool WillHandleTapEvent(const gfx::PointF& location, int tap_count);
 
   // To be called before forwarding a longpress event. This allows automatically
   // showing the selection or insertion handles from subsequent bounds changes.
   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();
 
   // Hide the handles and suppress bounds updates until the next explicit
   // showing allowance.
   void HideAndDisallowShowingAutomatically();
 
   // Override the handle visibility according to |hidden|.
   void SetTemporarilyHidden(bool hidden);
@@ skipping 122 matching lines @@
   // Whether a selection handle was dragged during the current 'selection
   // session' - i.e. since the current selection has been activated.
   bool selection_handle_dragged_;
 
   DISALLOW_COPY_AND_ASSIGN(TouchSelectionController);
 };
 
 }  // namespace ui
 
 #endif  // UI_TOUCH_SELECTION_TOUCH_SELECTION_CONTROLLER_H_