Make the SigninGlobalError multi-login aware.

BUG=277149
R=asvitkine@chromium.org, atwilson@chromium.org, courage@chromium.org, fgorski@chromium.org
TBR=asvitkine@chromium.org

Review URL: https://codereview.chromium.org/23875028

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225847 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225847