Don't let an active network attacker play tricks with CONNECT tunnels throgh proxy servers.
R=darin,wtc,eroman
BUG=7338
Review URL: http://codereview.chromium.org/27198
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@10595 0039d316-1c4b-4281-b951-d872f2087c98