Do not mutate ui::Event properties during nested event processing

ui/events/event.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_H_
 #define UI_EVENTS_EVENT_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/event_types.h"
@@ skipping 11 matching lines @@
 
 namespace gfx {
 class Transform;
 }
 
 namespace ui {
 class EventTarget;
 
 class EVENTS_EXPORT Event {
  public:
+  static scoped_ptr<Event> Clone(const Event& event);
+
   virtual ~Event();
 
   class DispatcherApi {
    public:
     explicit DispatcherApi(Event* event) : event_(event) {}
 
     void set_target(EventTarget* target) {
       event_->target_ = target;
     }
 
@@ skipping 733 matching lines @@
 
   const GestureEventDetails& details() const { return details_; }
 
  private:
   GestureEventDetails details_;
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_EVENT_H_