Merge "PersistableBundle.restoreFromXml should return a mutable bundle." am: ffb1899ba2

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1679293

Change-Id: I1aa7e3991da8461f31a6149babb8638aa4c35931

core/java/android/os/PersistableBundle.java

@@ -302,7 +302,7 @@ public final class PersistableBundle extends BaseBundle implements Cloneable, Pa
                         new MyReadMapCallback()));
             }
         }
-        return EMPTY;
+        return new PersistableBundle();  // An empty mutable PersistableBundle
     }
 
     @Override