report notification load on panel reveal

Counts may differ from user perception. For example, if notifications arrive
after the shade is open (even if it is only peeking) there will not be another
panel_reveal before the user sees the shade.  User perception is more accurately
measured by visibility events.

Peek events will report the notificaiton load as 1.

Bug: 20088581
Change-Id: I10221d4b66a18c223aae21e616615f087c65b1e1
diff --git a/services/core/java/com/android/server/EventLogTags.logtags b/services/core/java/com/android/server/EventLogTags.logtags
index 43b640b..76afab3 100644
--- a/services/core/java/com/android/server/EventLogTags.logtags
+++ b/services/core/java/com/android/server/EventLogTags.logtags
@@ -60,7 +60,7 @@
 2752 notification_cancel_all (uid|1|5),(pid|1|5),(pkg|3),(userid|1|5),(required_flags|1),(forbidden_flags|1),(reason|1|5),(listener|3)
 # when the notification panel is shown
 # Note: New tag range starts here since 2753+ have been used below.
-27500 notification_panel_revealed
+27500 notification_panel_revealed (items|1)
 # when the notification panel is hidden
 27501 notification_panel_hidden
 # when notifications are newly displayed on screen, or disappear from screen