API CHANGE: Backup/restore API changes requested by the API Council

* @hide the android.app.backup.RestoreSession class and functionality

* Provide a public method on android.app.backup.BackupManager that apps
  can use to request a restore pass of their last-known-good dataset.
  The new method is called requestRestore().

* Provide the name of the package being restored, not just its ordinal,
  in the RestoreObserver's onUpdate() callback.

Part of bug #2545514

Change-Id: I9689bf8d6e2b808b4ee412424a36a835be0a5ca8

services/java/com/android/server/BackupManagerService.java

@@ -1618,7 +1618,7 @@ class BackupManagerService extends IBackupManager.Stub {
 
                     if (mObserver != null) {
                         try {
-                            mObserver.onUpdate(count);
+                            mObserver.onUpdate(count, packageName);
                         } catch (RemoteException e) {
                             Slog.d(TAG, "Restore observer died in onUpdate");
                             mObserver = null;