aura: Start using EventPrcessor interface for event dispatch.

ui/events/event_processor.cc

 // Copyright 2013 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_processor.h"
 
 #include "ui/events/event_target.h"
 #include "ui/events/event_targeter.h"
 
 namespace ui {
 
 EventDispatchDetails EventProcessor::OnEventFromSource(Event* event) {
   EventTarget* root = GetRootTarget();
   CHECK(root);
   EventTargeter* targeter = root->GetEventTargeter();
   CHECK(targeter);
+  PrepareEventForDispatch(event);
   EventTarget* target = targeter->FindTargetForEvent(root, event);
   if (!target)
     return EventDispatchDetails();
 
   return DispatchEvent(target, event);
 }
 
+void EventProcessor::PrepareEventForDispatch(Event* event) {
+}
+
 }  // namespace ui