A follow-up of r64178.

Check for TLS 1.1 and TLS 1.2 (not yet supported)
version numbers to be future-proof.

Avoid a null pointer dereference when SSL client
authentication is used with SSL 2.0.  This will
be removed when we remove SSL 2.0 support.

Define the SSL_CONNECTION_VERSION_xxx enum constants
separately so we can assert their values are in range
at compile time.

R=eroman
BUG=53659
TEST=none
Review URL: http://codereview.chromium.org/4211006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@64814 0039d316-1c4b-4281-b951-d872f2087c98