GitLab

The popup collection was not handling correctly the case where it tells
the message center to mark its popups read, causing a NOTREACHED in
observer list.

BUG=324142

Review URL: https://codereview.chromium.org/99543003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238515 0039d316-1c4b-4281-b951-d872f2087c98