aura: Start using EventPrcessor interface for event dispatch.

ui/events/event_processor.cc

Index: ui/events/event_processor.cc
diff --git a/ui/events/event_processor.cc b/ui/events/event_processor.cc
index 45fa8302cada58da4cdd4232a4a7e8477173f3ff..1a50d2b7411221c63dc14b376f499102f259896e 100644
--- a/ui/events/event_processor.cc
+++ b/ui/events/event_processor.cc
@@ -14,6 +14,7 @@ EventDispatchDetails EventProcessor::OnEventFromSource(Event* event) {
   CHECK(root);
   EventTargeter* targeter = root->GetEventTargeter();
   CHECK(targeter);
+  PrepareEventForDispatch(event);
   EventTarget* target = targeter->FindTargetForEvent(root, event);
   if (!target)
     return EventDispatchDetails();
@@ -21,4 +22,7 @@ EventDispatchDetails EventProcessor::OnEventFromSource(Event* event) {
   return DispatchEvent(target, event);
 }
 
+void EventProcessor::PrepareEventForDispatch(Event* event) {
+}
+
 }  // namespace ui