rAc: improve loading screen sizing methodology

Moves more logic into the controller and improves behavior when the Loading... screen is showing due to a user changing the active wallet account (which is only possible with multi login).

BUG=259543

Review URL: https://codereview.chromium.org/26341003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228086 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228086
Permit NTLM token on cross-domain images.

The change in http://crrev.com/209100 is too general; this makes
the effects specific to embedded identities.

BUG=303046
R=cbentzel@chromium.org

Review URL: https://codereview.chromium.org/26745002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228087 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228087