GitLab

This is a re-implementation of extensions::AccountTracker, built on
IdentityProvider instead of SigninManager and
ProfileOAuth2TokenService. Removing the dependency on chrome/browser
will allow GCM to use this code.

BUG=374988

Review URL: https://codereview.chromium.org/336253002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@278476 0039d316-1c4b-4281-b951-d872f2087c98