Backup Wifi supplicant data.

WifiService requests a backup when it writes wifi configuration to disk.
Backup the wifi supplicant file when settings provider runs backup.
diff --git a/services/java/com/android/server/WifiService.java b/services/java/com/android/server/WifiService.java
index f5e2e3d..beadc5f 100644
--- a/services/java/com/android/server/WifiService.java
+++ b/services/java/com/android/server/WifiService.java
@@ -49,6 +49,7 @@
 import android.os.PowerManager;
 import android.os.Process;
 import android.os.RemoteException;
+import android.os.ServiceManager;
 import android.provider.Settings;
 import android.util.Log;
 import android.text.TextUtils;
@@ -64,6 +65,7 @@
 import java.io.PrintWriter;
 
 import com.android.internal.app.IBatteryStats;
+import android.backup.IBackupManager;
 import com.android.server.am.BatteryStatsService;
 
 /**
@@ -1436,6 +1438,16 @@
                 }
             }
         }
+        // Inform the backup manager about a data change
+        IBackupManager ibm = IBackupManager.Stub.asInterface(
+                ServiceManager.getService(Context.BACKUP_SERVICE));
+        if (ibm != null) {
+            try {
+                ibm.dataChanged("com.android.providers.settings");
+            } catch (Exception e) {
+                // Try again later
+            }
+        }
         return result;
     }