Make sure WindowObservers are removed from window before destruction

ui/aura/window_observer.cc

Index: ui/aura/window_observer.cc
diff --git a/ui/aura/input_state_lookup.cc b/ui/aura/window_observer.cc
similarity index 54%
copy from ui/aura/input_state_lookup.cc
copy to ui/aura/window_observer.cc
index 86ab3cd6587a009e063097c93533125882418aa5..d11a3f65244955f8c57bd9b697c3ffcf732ec213 100644
--- a/ui/aura/input_state_lookup.cc
+++ b/ui/aura/window_observer.cc
@@ -2,15 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "ui/aura/input_state_lookup.h"
+#include "ui/aura/window_observer.h"
 
-#include "base/logging.h"
+#include "ui/aura/window.h"
 
 namespace aura {
 
-// static
-scoped_ptr<InputStateLookup> InputStateLookup::Create() {
-  return scoped_ptr<InputStateLookup>();
+void WindowObserver::OnWindowDestroyed(Window* window) {
+  window->RemoveObserver(this);
 }
 
 }  // namespace aura