Purge Nonexistent User Jobs on Boot

In the case that a user has been removed but their jobs still exist on
disk, the JobSchedulerService will remove all jobs not associated with
current users on boot.
Exposed UserManagerService#getUserIds() via UserManagerInternal for
quick user id retrieval.

Fixes: 38261977
Test: manual

Change-Id: Id4b3c0a4142b4818fcd875eef18ea03f3c45ca40
Signed-off-by: Michael Wachenschwanz <mwachens@google.com>

core/java/android/os/UserManagerInternal.java

@@ -167,4 +167,12 @@ public abstract class UserManagerInternal {
      * Remove user's running state
      */
     public abstract void removeUserState(int userId);
+
+    /**
+     * Returns an array of user ids. This array is cached in UserManagerService and passed as a
+     * reference, so do not modify the returned array.
+     *
+     * @return the array of user ids.
+     */
+    public abstract int[] getUserIds();
 }