Calendar reminder pop-up while screen is off results in secrets being visible when screen is turned back on

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Be viewing secrets (I was in a secret's detail view, FWIW)
2. Turn phone display off
3. Let time pass
4. Have phone remind you of a google calendar event that has a reminder set to 
"pop up"
5. Turn on phone screen

Expected: calendar reminder popup is drawn over Secrets' "Enter password" UI
Actual: calendar reminder popup is drawn over the view in #1 above, and secret 
information can be seen.

This is a Nexus5 running a dogfood build of KK.

Original issue reported on code.google.com by [email protected] on 6 Jan 2014 at 10:00