Add a new GetTlsUniqueChannelBinding method to SSLSocket, and implement nss version.

net/socket/socket_test_util.cc

Index: net/socket/socket_test_util.cc
diff --git a/net/socket/socket_test_util.cc b/net/socket/socket_test_util.cc
index ff66830230ad73c2efb139795a2f191a7812f667..07cf20dcf8bb959d726b3107547a9b142e4b6259 100644
--- a/net/socket/socket_test_util.cc
+++ b/net/socket/socket_test_util.cc
@@ -717,6 +717,11 @@ int MockClientSocket::ExportKeyingMaterial(const base::StringPiece& label,
   return OK;
 }
 
+int MockClientSocket::GetTLSUniqueChannelBinding(std::string* out) {
+  out->append("MOCK_TLS_UNIQUE");

[wtc, 2012/07/30 22:42:26]

We should use out->assign() instead of out->append().

To be realistic, the mock tls-unique string should be
12-character long.

[Ryan Hamilton, 2012/07/31 16:12:21]

Done.

+  return OK;
+}
+
 ServerBoundCertService* MockClientSocket::GetServerBoundCertService() const {
   NOTREACHED();
   return NULL;