Revert 202821 &quotProtect WebURLLoaderImpl::Context while receiving...&quot

      > Protect WebURLLoaderImpl::Context while receiving responses.
> 
> A client's didReceiveResponse can cancel a request; by protecting the
> Context we avoid a use after free in this case.
> 
> Interestingly, we really had very good warning about this problem, see 
> https://codereview.chromium.org/11900002/ back in January.
> 
> R=darin
> BUG=241139
> 
> Review URL: https://chromiumcodereview.appspot.com/15738007

TBR=gavinp@chromium.org

Review URL: https://codereview.chromium.org/15859009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@202835 0039d316-1c4b-4281-b951-d872f2087c98