Refactor AccelerometerReader to provide an Observer

ash/accelerometer/accelerometer_observer.h

-// Copyright 2014 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_ACCELEROMETER_ACCELEROMETER_OBSERVER_H_
-#define ASH_ACCELEROMETER_ACCELEROMETER_OBSERVER_H_
-
-#include "ash/ash_export.h"
-#include "ui/accelerometer/accelerometer_types.h"
-
-namespace ash {
-
-// The interface for classes which observe accelerometer updates.
-class ASH_EXPORT AccelerometerObserver {
- public:
-  // Invoked when an accelerometer reading has been taken. The |update| can
-  // contain readings from one or more AccelerometerSources.
-  virtual void OnAccelerometerUpdated(
-      const ui::AccelerometerUpdate& update) = 0;
-
- protected:
-  virtual ~AccelerometerObserver() {}
-};
-
-}  // namespace ash
-
-#endif  // ASH_ACCELEROMETER_ACCELEROMETER_OBSERVER_H_