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

ui/events/event_dispatcher_unittest.cc

Index: ui/events/event_dispatcher_unittest.cc
diff --git a/ui/events/event_dispatcher_unittest.cc b/ui/events/event_dispatcher_unittest.cc
index 248784a8870c67c552a5d425475a630acd08cd9c..480ff6485f9e0a1aa3958b1eebe4a39c87321fb5 100644
--- a/ui/events/event_dispatcher_unittest.cc
+++ b/ui/events/event_dispatcher_unittest.cc
@@ -125,8 +125,10 @@ class NonCancelableEvent : public Event {
 
   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.