Add web socket command to stop serving a directory.

sdk/lib/_internal/pub/test/serve/web_socket/unserve_directory_responds_with_id_test.dart

Index: sdk/lib/_internal/pub/test/serve/web_socket/unserve_directory_responds_with_id_test.dart
diff --git a/sdk/lib/_internal/pub/test/serve/web_socket/serve_directory_responds_with_id_test.dart b/sdk/lib/_internal/pub/test/serve/web_socket/unserve_directory_responds_with_id_test.dart
similarity index 64%
copy from sdk/lib/_internal/pub/test/serve/web_socket/serve_directory_responds_with_id_test.dart
copy to sdk/lib/_internal/pub/test/serve/web_socket/unserve_directory_responds_with_id_test.dart
index e812e19a1cf3361bedecb66b3af7827c49781459..20a4d2acd5e9bf54b6351cabe7bd428d3b62f70c 100644
--- a/sdk/lib/_internal/pub/test/serve/web_socket/serve_directory_responds_with_id_test.dart
+++ b/sdk/lib/_internal/pub/test/serve/web_socket/unserve_directory_responds_with_id_test.dart
@@ -11,7 +11,7 @@ import '../utils.dart';
 
 main() {
   initConfig();
-  integration("serveDirectory includes id in response if given", () {
+  integration("unserveDirectory includes id in response if given", () {
     d.dir(appPath, [
       d.appPubspec(),
       d.dir("example", [
@@ -22,12 +22,16 @@ main() {
       ])
     ]).create();
 
-    pubServe();
+    // TODO(rnystrom): "example" is in here so that that's the port the web
+    // socket is bound to. That way, when we unserve "web", we don't close the
+    // web socket connection itself.
+    // Remove this when #16957 is fixed.
+    pubServe(args: ["example", "web"]);
 
     expectWebSocketCall({
-      "command": "serveDirectory",
+      "command": "unserveDirectory",
       "id": 12345,
-      "path": "example"
+      "path": "web"
     }, replyMatches: containsPair("id", 12345));
 
     endPubServe();