add test for remote flow sources in WebSockets

javascript/ql/test/library-tests/frameworks/WebSocket/test.expected

@@ -30,3 +30,6 @@ taintStep
 | server.js:11:11:11:27 | 'Hi from server!' | client.js:10:37:10:40 | data |
 | sockjs.js:11:20:11:50 | JSON.st ... .test)) | browser.js:25:26:25:31 | e.data |
 | sockjs.js:11:20:11:50 | JSON.st ... .test)) | browser.js:30:42:30:51 | event.data |
+remoteFlow
+| server.js:7:38:7:44 | message |
+| sockjs.js:9:31:9:37 | message |

javascript/ql/test/library-tests/frameworks/WebSocket/test.ql

@@ -15,3 +15,5 @@ query ServerWebSocket::ReceiveNode serverReceive() { any() }
 query predicate taintStep(DataFlow::Node pred, DataFlow::Node succ) {
   any(DataFlow::AdditionalFlowStep s).step(pred, succ)
 }
+
+query RemoteFlowSource remoteFlow() { any() }