Set unregistered handles to NULL in BatteryStatusObserver::Stop

device/battery/battery_status_manager_win.cc

Index: device/battery/battery_status_manager_win.cc
diff --git a/device/battery/battery_status_manager_win.cc b/device/battery/battery_status_manager_win.cc
index adda9d0c1c63c09f930fa01979bfb054bc52887c..6ad13da8a4b6e68c2711d6271d69eb4ba622a4eb 100644
--- a/device/battery/battery_status_manager_win.cc
+++ b/device/battery/battery_status_manager_win.cc
@@ -83,10 +83,14 @@ class BatteryStatusObserver {
   }
 
   void Stop() {
-    if (power_handle_)
+    if (power_handle_) {
       UnregisterNotification(power_handle_);
-    if (battery_change_handle_)
+      power_handle_ = NULL;
+    }
+    if (battery_change_handle_) {
       UnregisterNotification(battery_change_handle_);
+      battery_change_handle_ = NULL;
+    }
     window_.reset();
   }