chromeos: Add power supply info reading capability

chrome/browser/chromeos/dbus/power_manager_client.h

 // Copyright (c) 2011 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_DBUS_POWER_MANAGER_CLIENT_H_
 #define CHROME_BROWSER_CHROMEOS_DBUS_POWER_MANAGER_CLIENT_H_
 
 #include "base/memory/ref_counted.h"
 #include "base/observer_list.h"
 
 #include <string>
 
 namespace dbus {
 class Bus;
 class ObjectProxy;
 class Response;
 class Signal;
 }  // namespace
 
 namespace chromeos {
 
+struct PowerStatus;
+
 // PowerManagerClient is used to communicate with the power manager.
 class PowerManagerClient {
  public:
   // Interface for observing changes from the power manager.
   class Observer {
    public:
     // Called when the brightness is changed.
     // |level| is of the range [0, 100].
     // |user_initiated| is true if the action is initiated by the user.
-    virtual void BrightnessChanged(int level, bool user_initiated) = 0;
+    virtual void BrightnessChanged(int level, bool user_initiated) {}
+
+    // Called when power supply polling takes place.  |status| is a data
+    // structure that contains the current state of the power supply.
+    virtual void UpdatePowerStatus(const chromeos::PowerStatus& status) {}
   };
 
   // Adds and removes the observer.
   virtual void AddObserver(Observer* observer) = 0;
   virtual void RemoveObserver(Observer* observer) = 0;
 
   // Decreases the screen brightness. |allow_off| controls whether or not
   // it's allowed to turn off the back light.
   virtual void DecreaseScreenBrightness(bool allow_off) = 0;
 
   // Increases the screen brightness.
   virtual void IncreaseScreenBrightness() = 0;
 
   // Creates the instance.
   static PowerManagerClient* Create(dbus::Bus* bus);
 
   PowerManagerClient();
   virtual ~PowerManagerClient();
 
   DISALLOW_COPY_AND_ASSIGN(PowerManagerClient);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_DBUS_POWER_MANAGER_CLIENT_H_