net: Disconnect proxy sockets that have a certificate error.

      BUG=116398
TEST=Set a SPDY proxy with a certificate error. Ensure that requests always get ERR_PROXY_CERTIFICATE_INVALID, even with several reloads.


Review URL: http://codereview.chromium.org/9600022

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@124970 0039d316-1c4b-4281-b951-d872f2087c98