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

net/socket/ssl_client_socket_win.cc

Index: net/socket/ssl_client_socket_win.cc
diff --git a/net/socket/ssl_client_socket_win.cc b/net/socket/ssl_client_socket_win.cc
index d9973800707e0e243258cc0875484dba5f0d8609..5aee040f6e6b8d0bab27490b0bfdbeec42dec0a3 100644
--- a/net/socket/ssl_client_socket_win.cc
+++ b/net/socket/ssl_client_socket_win.cc
@@ -554,6 +554,10 @@ int SSLClientSocketWin::ExportKeyingMaterial(const base::StringPiece& label,
   return ERR_NOT_IMPLEMENTED;
 }
 
+int SSLClientSocketOpenSSL::GetTLSUniqueChannelBinding(std::string* out) {
+  return ERR_NOT_IMPLEMENTED;
+}
+
 SSLClientSocket::NextProtoStatus
 SSLClientSocketWin::GetNextProto(std::string* proto,
                                  std::string* server_protos) {