chromeos: Show onscreen bubble when brightness changes.

chrome/browser/chromeos/cros/brightness_library.h

+// Copyright (c) 2010 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 CHROME_BROWSER_CHROMEOS_CROS_BRIGHTNESS_LIBRARY_H_
+#define CHROME_BROWSER_CHROMEOS_CROS_BRIGHTNESS_LIBRARY_H_
+#pragma once
+
+#include "cros/chromeos_brightness.h"
+
+namespace chromeos {
+
+class BrightnessLibrary {
+ public:
+  class Observer {
+   public:
+    virtual void BrightnessChanged(int level) = 0;
+  };
+
+  virtual ~BrightnessLibrary() {}
+
+  virtual void AddObserver(Observer* observer) = 0;
+  virtual void RemoveObserver(Observer* observer) = 0;
+
+  // Factory function, creates a new instance and returns ownership.
+  // For normal usage, access the singleton via CrosLibrary::Get().
+  static BrightnessLibrary* GetImpl(bool stub);
+};
+
+}  // namespace chromeos
+
+#endif  // CHROME_BROWSER_CHROMEOS_CROS_BRIGHTNESS_LIBRARY_H_