mash: Move shelf_navigator.* to //ash/common/shelf

ash/shelf/shelf_navigator.h

-// 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.
-
-#ifndef ASH_SHELF_SHELF_NAVIGATOR_H_
-#define ASH_SHELF_SHELF_NAVIGATOR_H_
-
-#include "ash/ash_export.h"
-#include "ash/common/shelf/shelf_constants.h"
-
-namespace ash {
-
-class ShelfModel;
-
-// Scans the current shelf item and returns the index of the shelf item which
-// should be activated next for the specified |direction|. Returns -1 if fails
-// to find such item.
-ASH_EXPORT int GetNextActivatedItemIndex(const ShelfModel& model,
-                                         CycleDirection direction);
-
-}  // namespace ash
-
-#endif  // ASH_SHELF_SHELF_NAVIGATOR_H_