Add drive::JobScheduler::GetResourceEntry

Basically, just reverting crrev.com/225401

BUG=260542
TEST=unit_tests
R=kinaba@chromium.org

Review URL: https://codereview.chromium.org/68283002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234204 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234204