Add web socket command to stop serving a directory.

sdk/lib/_internal/pub/lib/src/barback/build_directory.dart

Index: sdk/lib/_internal/pub/lib/src/barback/build_directory.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/build_directory.dart b/sdk/lib/_internal/pub/lib/src/barback/build_directory.dart
new file mode 100644
index 0000000000000000000000000000000000000000..2c8cc19059f38cb621385148ee174900c8dc827e
--- /dev/null
+++ b/sdk/lib/_internal/pub/lib/src/barback/build_directory.dart
@@ -0,0 +1,54 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library pub.barback.build_environment;
+
+import 'dart:async';
+
+import 'package:watcher/watcher.dart';
+
+import 'build_environment.dart';
+import 'server.dart';
+
+/// A directory in the entrypoint package whose contents have been made
+/// available to barback and that are bound to a server.
+class BuildDirectory {
+  final BuildEnvironment _environment;
+
+  /// The relative directory path within the package.
+  final String directory;
+
+  /// The server bound to this directory.
+  BarbackServer get server => _server;
+  BarbackServer _server;
+
+  /// The subscription to the [DirectoryWatcher] used to watch this directory
+  /// for changes.
+  ///
+  /// If the directory is not being watched, this will be `null`.
+  StreamSubscription<WatchEvent> watchSubscription;
+
+  BuildDirectory(this._environment, this.directory);
+
+  /// Binds a server running on [hostname]:[port] to this directory.
+  Future<BarbackServer> serve(String hostname, int port) {
+    return BarbackServer.bind(_environment, hostname, port, directory)
+        .then((server) => _server = server);
+  }
+
+  /// Removes the build directory from the build environment.
+  ///
+  /// Closes the server, removes the assets from barback, and stops watching it.
+  Future close() {
+    var futures = [server.close()];
+
+    // Stop watching the directory.
+    if (watchSubscription != null) {
+      var cancel = watchSubscription.cancel();
+      if (cancel != null) futures.add(cancel);
+    }
+
+    return Future.wait(futures);
+  }
+}