Fix race in listening to session stop signal.

BUG=chromium:344173
TEST=trybot

Change-Id: I8e915236a4aee79f4dbd8afe78597980b4617e3b
Reviewed-on: https://chromium-review.googlesource.com/186847
Reviewed-by: Chris Masone <cmasone@chromium.org>
Commit-Queue: Achuith Bhandarkar <achuith@chromium.org>
Tested-by: Achuith Bhandarkar <achuith@chromium.org>
1 file changed