GitLab

Change RunTaskOnThread's argument type from MessageLoopProxy to SingleThreadTaskRunner in favor of generality
Move CreateErrorRunCallback to its exclusive user job_scheduler.cc

BUG=None
TEST=unit_tests

Review URL: https://codereview.chromium.org/77553006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236998 0039d316-1c4b-4281-b951-d872f2087c98