GitLab

There's a rare crash in ChromeLauncherController that looks
like a user is switching into Ash with no profile and a
read-only profile directory. Add a CHECK to figure out how
common this problem is.

BUG=383019
TEST=none

Review URL: https://codereview.chromium.org/336603002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@276868 0039d316-1c4b-4281-b951-d872f2087c98