Fix GuardedBy analysis.

Removes false positives as detected by error prone.

Change-Id: I14cdb56384850b3d4af7e58c6e5cdcd1391aa61a
diff --git a/src/com/android/providers/downloads/DownloadNotifier.java b/src/com/android/providers/downloads/DownloadNotifier.java
index 60c249f..3b57437 100644
--- a/src/com/android/providers/downloads/DownloadNotifier.java
+++ b/src/com/android/providers/downloads/DownloadNotifier.java
@@ -122,6 +122,7 @@
         }
     }
 
+    @GuardedBy("mActiveNotifs")
     private void updateWithLocked(Collection<DownloadInfo> downloads) {
         final Resources res = mContext.getResources();