exo: Fix multi-display hardware cursor

ui/aura/client/cursor_client_observer.h

 // Copyright (c) 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.
 
 #ifndef UI_AURA_CLIENT_CURSOR_CLIENT_OBSERVER_H_
 #define UI_AURA_CLIENT_CURSOR_CLIENT_OBSERVER_H_
 
 #include "ui/aura/aura_export.h"
 #include "ui/base/cursor/cursor.h"
 
+namespace display {
+class Display;
+}
+
 namespace aura {
 namespace client {
 
 class AURA_EXPORT CursorClientObserver {
  public:
   virtual void OnCursorVisibilityChanged(bool is_visible) {}
   virtual void OnCursorSetChanged(ui::CursorSetType cursor_set) {}
+  virtual void OnCursorDisplayChanged(const display::Display& display) {}
 
  protected:
   virtual ~CursorClientObserver() {}
 };
 
 }  // namespace client
 }  // namespace aura
 
 #endif  // UI_AURA_CLIENT_CURSOR_CLIENT_OBSERVER_H_