Refactor CopyNativeEvent and add events_mac.mm to start implementing stubs

ui/events/x/events_x.cc

Index: ui/events/x/events_x.cc
diff --git a/ui/events/x/events_x.cc b/ui/events/x/events_x.cc
index bf8b04ee58b0cde6d9036d3d5840b84869b8672a..b57eec1e807b21aa28372e63c675d6bab7843508 100644
--- a/ui/events/x/events_x.cc
+++ b/ui/events/x/events_x.cc
@@ -534,6 +534,16 @@ gfx::Vector2d GetMouseWheelOffset(const base::NativeEvent& native_event) {
   }
 }
 
+base::NativeEvent CopyNativeEvent(const base::NativeEvent& event) {
+  if (!event || event->type == GenericEvent)
+    return NULL;
+  XEvent* copy = new XEvent;
+  *copy = *event;
+  return copy;
+}
+
+void ReleaseCopiedNativeEvent(const base::NativeEvent& event) { delete event; }
+
 void ClearTouchIdIfReleased(const base::NativeEvent& xev) {
   ui::EventType type = ui::EventTypeFromNative(xev);
   if (type == ui::ET_TOUCH_CANCELLED ||