chromeos: Add power supply info reading capability

chrome/browser/chromeos/dbus/power_manager_client.h

Index: chrome/browser/chromeos/dbus/power_manager_client.h
diff --git a/chrome/browser/chromeos/dbus/power_manager_client.h b/chrome/browser/chromeos/dbus/power_manager_client.h
index e2e858873435ad1da0573140aaba07bcfb8e1147..39845cff0b84bb0c3b36515088b5d484ed18f507 100644
--- a/chrome/browser/chromeos/dbus/power_manager_client.h
+++ b/chrome/browser/chromeos/dbus/power_manager_client.h
@@ -19,6 +19,8 @@ class Signal;
 
 namespace chromeos {
 
+struct PowerStatus;
+
 // PowerManagerClient is used to communicate with the power manager.
 class PowerManagerClient {
  public:
@@ -28,7 +30,11 @@ class PowerManagerClient {
     // 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.