Fix crash when locking a profile. The crash is happening because navigating to a URL triggers the signin header helper code. Since locking shouldn't actually do a Gaia logout, I'm removing all the code related to that.

NOTRY-ing because it's been a week of "extension "RANDR" missing on display ":9" bot errors. 

BUG=NONE
TBR=pkasting@chromium.org
NOTRY=TRUE

Review URL: https://codereview.chromium.org/64313005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235801 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 235801