Updating certain services to be final fields.

Certain services were removed from being final fields in ag/5932642.
This change essentially reverts the deletions of those final fields.

Bug: 122591875
Test: atest cts.tests.app.src.android.app.cts.ActivityManagerTest#testIsAppForegroundRemoved
Change-Id: I403d214b31c964ee5587c35260138e0af12fd11e
diff --git a/services/backup/java/com/android/server/backup/UserBackupManagerService.java b/services/backup/java/com/android/server/backup/UserBackupManagerService.java
index 6b0adfb..fb6b70f 100644
--- a/services/backup/java/com/android/server/backup/UserBackupManagerService.java
+++ b/services/backup/java/com/android/server/backup/UserBackupManagerService.java
@@ -249,11 +249,11 @@
     private final TransportManager mTransportManager;
     private final HandlerThread mUserBackupThread;
 
-    private Context mContext;
-    private PackageManager mPackageManager;
-    private IPackageManager mPackageManagerBinder;
-    private IActivityManager mActivityManager;
-    private ActivityManagerInternal mActivityManagerInternal;
+    private final Context mContext;
+    private final PackageManager mPackageManager;
+    private final IPackageManager mPackageManagerBinder;
+    private final IActivityManager mActivityManager;
+    private final ActivityManagerInternal mActivityManagerInternal;
     private PowerManager mPowerManager;
     private final AlarmManager mAlarmManager;
     private final IStorageManager mStorageManager;