Give the RequestFetcher access to cross-origin URLs when allowed

Previously even if the URL loader was configured to have cross origin access
this bit was not sent through to the RequestFetcher so that access could be
granted. This CL adds that information to the FetchRequest so that
RequestFetcher::canRequest gives the correct result in these cases.

BUG=386920

Review URL: https://codereview.chromium.org/344883006

git-svn-id: svn://svn.chromium.org/blink/trunk@178029 bbb929c8-8fbe-4397-9dbb-9b2b20218538