Remove the speculative resource prefetching code. This was experimental code added 1.5 years ago and not used for the last year.

BUG=164207,304341
R=cbentzel@chromium.org

Review URL: https://codereview.chromium.org/117933003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243098 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243098