Eliminate usage of PO2TS::GetPrimaryAccountID() in UbertokenFetcher.

This change is a first step toward moving UbertokenFetcher and
GoogleAutoLoginHelper into //google_apis. Rather than UbertokenFetcher having a
variant of StartFetchingToken() wherein it uses the primary account ID,
callers must always supply the account ID. As GoogleAutoLoginHelper should
also not know about PO2TS, this CL similarly eliminates
GoogleAutoLoginHelper::Login().

BUG=330292
TBR=nyquist,mkwst,courage

Review URL: https://codereview.chromium.org/131973004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244208 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244208