Revert 244591 "Move refresh_tokens_ to MutableProfileOAuth2Token..."

Top crasher in canary. See bug 334251.

> Move refresh_tokens_ to MutableProfileOAuth2TokenService.
> 
> This CL moves refresh_tokens_ from ProfileOAuth2TokenService to
> MutableProfileOAuth2TokenService. It also removes some unused private
> methods from ProfileOAuth2TokenService.
> 
> R=rogerta
> TBR=sky, rohitrao
> BUG=320625
> 
> Review URL: https://codereview.chromium.org/114513003

TBR=msarda@chromium.org

Review URL: https://codereview.chromium.org/132993006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244810 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244810