Should not use empty scope set when requesting an access token.
An empty scope means "give me the login-scoped access token", which is likely
over scoped and not allowed on android anyway.

BUG=339883
R=nyquist@chromium.org

Review URL: https://codereview.chromium.org/154583002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249149 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249149