Recycled existing OAuthLogin-scoped access token for new accounts.

BUG=329411
TEST=OAuth2.*

Review URL: https://codereview.chromium.org/105663003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241832 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241832