drive: Add UserContext argument to JobScheduler::UpdateResource

BUG=331981
TEST=unit_tests

Review URL: https://codereview.chromium.org/110273005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243284 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243284