Revert 246456 "Support sending client certificates when validati..."

> Support sending client certificates when validating tokens.
> 
> I chose to add a new certificate auto-selection policy, because the existing certificate auto-selection is very coupled with Chrome. The existing AutoSelectCertificateUrls requires chrome/common/content_settings_pattern.h (which depends on other browser specific files, and is otherwise very browser-specific logic) to parse the URL pattern, and chrome/browser/chrome_content_browser_client.cc to match the certificate.
> 
> Also, URLFetcher doesn't support sending certificates, and supporting it is a strict non-goal ( https://codereview.chromium.org/136883010/ ), so I had to use the lower level URLRequest, and have tokenvalidator do its own buffering.
> 
> Finally, the client certificate store has some unpleasant lifetime requirements, so there are some hacks to deal with that as well.
> 
> BUG=315825
> 
> Review URL: https://codereview.chromium.org/133273025

TBR=rmsousa@chromium.org

Review URL: https://codereview.chromium.org/145413002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246464 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246464