Fix crash which occurs when a widget destroys itself as a result of ET_GESTURE_TAP_DOWN

ui/views/widget/root_view.h

 // Copyright (c) 2012 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_VIEWS_WIDGET_ROOT_VIEW_H_
 #define UI_VIEWS_WIDGET_ROOT_VIEW_H_
 
 #include <string>
 
 #include "base/memory/ref_counted.h"
@@ skipping 127 matching lines @@
   // cursor during drag operations. The location of the mouse should be in the
   // current coordinate system (i.e. any necessary transformation should be
   // applied to the point prior to calling this).
   void UpdateCursor(const ui::MouseEvent& event);
 
   // Updates the last_mouse_* fields from e. The location of the mouse should be
   // in the current coordinate system (i.e. any necessary transformation should
   // be applied to the point prior to calling this).
   void SetMouseLocationAndFlags(const ui::MouseEvent& event);
 
-  void DispatchEventToTarget(View* target, ui::Event* event);
+  ui::EventDispatchDetails DispatchEventToTarget(
+      View* target,
+      ui::Event* event) WARN_UNUSED_RESULT;
 
   // |view| is the view receiving |event|. This function sends the event to all
   // the Views up the hierarchy that has |notify_enter_exit_on_child_| flag
   // turned on, but does not contain |sibling|.
   void NotifyEnterExitOfDescendant(const ui::MouseEvent& event,
                                    ui::EventType type,
                                    View* view,
                                    View* sibling);
 
   // Dispatches the KeyEvent to |view| and ancestors until the event is
@@ skipping 64 matching lines @@
   // Tracks drag state for a view.
   View::DragInfo drag_info_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(RootView);
 };
 
 }  // namespace internal
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_ROOT_VIEW_H_