GitLab

Currently a URLRequestJobFactory is optional, as the global
URLRequestJobManager passes jobs on to the URLRequestFilter and
global http/https/ws/wss factories.  In order to be able to
eliminate the global URLRequestJobManager object, first have to
give all contexts their own URLRequestJobFactory.

BUG=81979
TBR=ajwong@chromium.org (Who actually signed off on this, but Rietveld ignored his email).

Review URL: https://codereview.chromium.org/311393002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@276867 0039d316-1c4b-4281-b951-d872f2087c98