Get rid of Chain.track in pub.

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

Index: sdk/lib/_internal/pub/lib/src/barback/admin_server.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/admin_server.dart b/sdk/lib/_internal/pub/lib/src/barback/admin_server.dart
index c6fd86fdd030fdd94766dd92d65a6fd6229c324b..057a5888e91435ccca26a10c131a025d0e40b7f1 100644
--- a/sdk/lib/_internal/pub/lib/src/barback/admin_server.dart
+++ b/sdk/lib/_internal/pub/lib/src/barback/admin_server.dart
@@ -10,7 +10,6 @@ import 'dart:io';
 import 'package:http_parser/http_parser.dart';
 import 'package:shelf/shelf.dart' as shelf;
 import 'package:shelf_web_socket/shelf_web_socket.dart';
-import 'package:stack_trace/stack_trace.dart';
 
 import '../io.dart';
 import '../log.dart' as log;
@@ -30,7 +29,7 @@ class AdminServer extends BaseServer {
   /// Creates a new server and binds it to [port] of [host].
   static Future<AdminServer> bind(AssetEnvironment environment,
       String host, int port) {
-    return Chain.track(bindServer(host, port)).then((server) {
+    return bindServer(host, port).then((server) {
       log.fine('Bound admin server to $host:$port.');
       return new AdminServer._(environment, server);
     });