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

ui/events/event_dispatcher_unittest.cc

 // 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.
 
 #include "ui/events/event_dispatcher.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/events/event.h"
 #include "ui/events/event_dispatcher.h"
 #include "ui/events/event_target.h"
@@ skipping 107 matching lines @@
 
 class NonCancelableEvent : public Event {
  public:
   NonCancelableEvent()
       : Event(ui::ET_CANCEL_MODE, ui::EventTimeForNow(), 0) {
     set_cancelable(false);
   }
 
   virtual ~NonCancelableEvent() {}
 
- private:
-  DISALLOW_COPY_AND_ASSIGN(NonCancelableEvent);
+  // Event:
+  virtual scoped_ptr<Event> Clone() const OVERRIDE {
+    return scoped_ptr<Event>(new NonCancelableEvent(*this));
+  }
 };
 
 // Destroys the dispatcher-delegate when it receives any event.
 class EventHandlerDestroyDispatcherDelegate : public TestEventHandler {
  public:
   EventHandlerDestroyDispatcherDelegate(EventDispatcherDelegate* delegate,
                                         int id)
       : TestEventHandler(id),
         dispatcher_delegate_(delegate) {
   }
@@ skipping 460 matching lines @@
     NonCancelableEvent event;
     EventDispatchDetails details = dispatcher->ProcessEvent(&target, &event);
     EXPECT_TRUE(details.dispatcher_destroyed);
     EXPECT_EQ(2U, target.handler_list().size());
     EXPECT_EQ(1, target.handler_list()[0]);
     EXPECT_EQ(2, target.handler_list()[1]);
   }
 }
 
 }  // namespace ui