CrOS - Add certificate support to VPN UI.

CrOS - Add certificate support to VPN UI.

Adds support for user certificates, sending their PKCS#11 certificate ID down to flimflam.  Note this does not send the certificate slot - flimflam will have to look in the TPM slot.  This is similar to what we do for 802.1X Wi-Fi connection certificates.

BUG=chromium-os:14111
TEST=Start with no certificates installed.  Go to network menu > Private networks > Add private network.  Select "L2TPIPSec + User cert".  Verify connect button does not enable (because you have no certs available).  Cancel, then install a user cert with certificate manager.  Verify the cert appears in the Add private network dialog.  Verify connect button is enabled.  Verify you can connect to a VPN that requires certs.

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=86323

[James Cook, 2011-05-20 16:41:24]

Steven, please have a look.  Ken told me to just send the certificate ID, not
the cert slot, as flimflam will just assume these certs are in the TPM (like it
does with 802.1X).

CC Ken - just FYI.

[James Cook, 2011-05-20 18:42:06]

Charlie, Steven's out today and Monday - can you take a look?

[Charlie Lee, 2011-05-20 21:44:46]

LGTM with nits

http://codereview.chromium.org/7038038/diff/1/chrome/browser/chromeos/cros/ne...
File chrome/browser/chromeos/cros/network_library.cc (left):

http://codereview.chromium.org/7038038/diff/1/chrome/browser/chromeos/cros/ne...
chrome/browser/chromeos/cros/network_library.cc:476:
PROPERTY_INDEX_L2TPIPSEC_CERT,
is this still needed?

http://codereview.chromium.org/7038038/diff/1/chrome/browser/chromeos/options...
File chrome/browser/chromeos/options/vpn_config_view.cc (right):

http://codereview.chromium.org/7038038/diff/1/chrome/browser/chromeos/options...
chrome/browser/chromeos/options/vpn_config_view.cc:117: return
x509_certificate_model::GetPkcs11Id(cert_handle);
easier to just inline cert->os_cert_handle()