Experimental Revert of 231910 "Allows prefetch and other detachable requests to ...",
to see if it fixes 314726.

> Allows prefetch and other detachable requests to live beyond the renderer by delaying LinkLoader::Cancel requests by a few seconds and through the use of a new DetachedResourceHandler.
> 
> The general concept of a detachable resource should be useful for <a ping> as well.
> 
> BUG=286186,314726
> 
> Review URL: https://codereview.chromium.org/25772002

TBR=jkarlin@google.com

Review URL: https://codereview.chromium.org/58343003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232785 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232785