Get event targetting working for mouse events.

ui/aura/env.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/aura/env.h"
 
 #include "base/lazy_instance.h"
 #include "base/threading/thread_local.h"
 #include "ui/aura/env_observer.h"
 #include "ui/aura/input_state_lookup.h"
@@ skipping 93 matching lines @@
 // Env, ui::EventTarget implementation:
 
 bool Env::CanAcceptEvent(const ui::Event& event) {
   return true;
 }
 
 ui::EventTarget* Env::GetParentTarget() {
   return NULL;
 }
 
-scoped_ptr<ui::EventTargetIterator> Env::GetChildIterator() const {
+scoped_ptr<ui::EventTargetIterator> Env::GetChildIterator() {
   return scoped_ptr<ui::EventTargetIterator>();
 }
 
 ui::EventTargeter* Env::GetEventTargeter() {
   NOTREACHED();
   return NULL;
 }
 
 }  // namespace aura