Get rid of Chain.track in pub.

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

Index: sdk/lib/_internal/pub/lib/src/barback/base_server.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/base_server.dart b/sdk/lib/_internal/pub/lib/src/barback/base_server.dart
index 95dc355562341cbab81f716af11186c0107c24e1..cb23036f17a79bbabab63bc4133e68809c74d13c 100644
--- a/sdk/lib/_internal/pub/lib/src/barback/base_server.dart
+++ b/sdk/lib/_internal/pub/lib/src/barback/base_server.dart
@@ -11,7 +11,6 @@ import 'dart:io';
 import 'package:barback/barback.dart';
 import 'package:shelf/shelf.dart' as shelf;
 import 'package:shelf/shelf_io.dart' as shelf_io;
-import 'package:stack_trace/stack_trace.dart';
 
 import '../log.dart' as log;
 import '../utils.dart';
@@ -43,7 +42,7 @@ abstract class BaseServer<T> {
   final _resultsController = new StreamController<T>.broadcast();
 
   BaseServer(this.environment, this._server) {
-    shelf_io.serveRequests(Chain.track(_server), const shelf.Pipeline()
+    shelf_io.serveRequests(_server, const shelf.Pipeline()
         .addMiddleware(shelf.createMiddleware(errorHandler: _handleError))
         .addMiddleware(shelf.createMiddleware(responseHandler: _disableGzip))
         .addHandler(handleRequest));