NoMan: Log canceled notifications

In addition to logging cancelation command, also log actually
canceled notifications via the new eventlog tag notification_canceled.

Bug: 18083122
Change-Id: I1e3e1e1368f39519f34c002ae374f318f647a401
diff --git a/services/core/java/com/android/server/EventLogTags.logtags b/services/core/java/com/android/server/EventLogTags.logtags
index f7925f0..eec97f3 100644
--- a/services/core/java/com/android/server/EventLogTags.logtags
+++ b/services/core/java/com/android/server/EventLogTags.logtags
@@ -71,6 +71,8 @@
 27520 notification_clicked (key|3)
 # when a notification action button has been clicked
 27521 notification_action_clicked (key|3),(action_index|1)
+# when a notification has been canceled
+27530 notification_canceled (key|3),(reason|1)
 
 # ---------------------------
 # Watchdog.java