Implement client certificate support via SmartCard.

Updates SSLClientCertificateRequest such that certificate can retrieved
from Android store or external PKCS11 KeyStore

NOTRY=true
COLLABORATOR=ppi@chromium.org
BUG=341500

Review URL: https://codereview.chromium.org/147573005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250624 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250624