Reintroduce per-app scheduled job limits

There was a period of interim deployments during which sync-manager jobs
were not properly attributed to the package whose sync operations were
being driven.  This situation is now corrected when it is encountered.

Bug 27335118

Change-Id: Iafc40c80093499447b2e62a4888e3ece0371bfcb
diff --git a/services/core/java/com/android/server/job/JobSchedulerService.java b/services/core/java/com/android/server/job/JobSchedulerService.java
index bd888d8..fba7e7d 100644
--- a/services/core/java/com/android/server/job/JobSchedulerService.java
+++ b/services/core/java/com/android/server/job/JobSchedulerService.java
@@ -92,7 +92,7 @@
     /** The maximum number of concurrent jobs we run at one time. */
     private static final int MAX_JOB_CONTEXTS_COUNT = 8;
     /** Enforce a per-app limit on scheduled jobs? */
-    private static final boolean ENFORCE_MAX_JOBS = false;
+    private static final boolean ENFORCE_MAX_JOBS = true;
     /** The maximum number of jobs that we allow an unprivileged app to schedule */
     private static final int MAX_JOBS_PER_APP = 100;