Add LauncherIconObserver.

ash/launcher/launcher_icon_observer.h

+// 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.
+
+#ifndef ASH_LAUNCHER_LAUNCHER_ICON_OBSERVER_H_
+#define ASH_LAUNCHER_LAUNCHER_ICON_OBSERVER_H_
+#pragma once
+
+#include "base/basictypes.h"
+
+namespace ash {
+
+class ASH_EXPORT LauncherIconObserver {
+ public:
+  LauncherIconObserver() {}
+
+  // Invoked when any icon on launcher changes position.
+  virtual void OnLauncherIconPositionsChanged() = 0;
+
+ protected:
+  virtual ~LauncherIconObserver() {}
+
+  DISALLOW_COPY_AND_ASSIGN(LauncherIconObserver);
+};
+
+}  // namespace ash
+
+#endif  // ASH_LAUNCHER_LAUNCHER_ICON_OBSERVER_H_