Revert "Remove the SCHEME_AND_DOMAIN constant."

This reverts commit 8ddb9cfcb6.

tests/wpt/web-platform-tests/websockets/interfaces/WebSocket/protocol/protocol-initial.html

@@ -7,6 +7,6 @@
 <script>
 test(function(t) {
   // The protocol attribute must initially return the empty string
-  assert_equals((new WebSocket(SCHEME_DOMAIN_PORT + '/empty-message')).protocol, '');
+  assert_equals((new WebSocket(SCHEME_AND_DOMAIN+'/')).protocol, '');
 });
 </script>