Revert 269855 "Only commit cookie changes in prerenders after a ..."

Revert 269855 "Only commit cookie changes in prerenders after a ..."

This broke again - http://build.chromium.org/p/chromium.mac/buildstatus?builder=Mac%2010.7%20Tests%20%28dbg%29%281%29&number=23472

> Only commit cookie changes in prerenders after a prerender is shown
> Will create a PrerenderCookieStore for each prerender, retaining all cookie
> operations of a prerender until the prerender is shown to the user.
> Forces prerenders to be in a new render process by themselves for this to work.
> BUG=371003
>
> This is a resubmission of https://codereview.chromium.org/233353003, which had
> to be reverted due to build breaks. See LGTM's there.
>
> Review URL: https://codereview.chromium.org/278403003

TBR=tburkard@chromium.org

Review URL: https://codereview.chromium.org/280383002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@269879 0039d316-1c4b-4281-b951-d872f2087c98