Getting rid of GetDefaultProfile in kiosk_mode_screensaver.cc

This is part of the effort to get rid of the GetDefaultProfile effort.

BUG=322682
TEST=none

Review URL: https://codereview.chromium.org/112123002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240007 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240007