Get event targetting working for mouse events.

ui/events/event_target.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_EVENTS_EVENT_TARGET_H_
 #define UI_EVENTS_EVENT_TARGET_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
@@ skipping 29 matching lines @@
   EventTarget();
   ~EventTarget() override;
 
   virtual bool CanAcceptEvent(const Event& event) = 0;
 
   // Returns the parent EventTarget in the event-target tree.
   virtual EventTarget* GetParentTarget() = 0;
 
   // Returns an iterator an EventTargeter can use to iterate over the list of
   // child EventTargets.
-  virtual scoped_ptr<EventTargetIterator> GetChildIterator() const = 0;
+  virtual scoped_ptr<EventTargetIterator> GetChildIterator() = 0;
 
   // Returns the EventTargeter that should be used to find the target for an
   // event in the subtree rooted at this EventTarget.
   virtual EventTargeter* GetEventTargeter() = 0;
 
   // Updates the states in |event| (e.g. location) to be suitable for |target|,
   // so that |event| can be dispatched to |target|.
   virtual void ConvertEventToTarget(EventTarget* target,
                                     LocatedEvent* event);
 
@@ skipping 48 matching lines @@
   EventHandlerList pre_target_list_;
   EventHandlerList post_target_list_;
   EventHandler* target_handler_;
 
   DISALLOW_COPY_AND_ASSIGN(EventTarget);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_EVENT_TARGET_H_