Fix crash when opening the avatar bubble in Guest mode.

BUG=NONE
TEST=With --new-profile-management enabled, open a guest browser window and click on the avatar button. The bubble should come up.

Review URL: https://codereview.chromium.org/64793002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233821 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233821