Include file path in JSON error when possible.

sdk/lib/_internal/pub/test/serve/utils.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.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_tests;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
@@ skipping 325 matching lines @@
 
   return WebSocket.connect("ws://localhost:$_adminPort").then((socket) {
     _webSocket = socket;
     // TODO(rnystrom): Works around #13913.
     _webSocketBroadcastStream = _webSocket.map(JSON.decode).asBroadcastStream();
   });
 }
 
 /// Schedules closing the web socket connection to the currently-running pub
 /// serve.
-Future closeWebSocket() {
+void closeWebSocket() {
   schedule(() {
     return _ensureWebSocket().then((_) => _webSocket.close())
         .then((_) => _webSocket = null);
   }, "closing web socket");
 }
 
 /// Sends a JSON RPC 2.0 request to the running pub serve's web socket
 /// connection.
 ///
 /// This calls a method named [method] with the given [params] (or no
@@ skipping 133 matching lines @@
 /// included. Unlike [getServerUrl], this should only be called after the ports
 /// are known.
 String _getServerUrlSync([String root, String path]) {
   if (root == null) root = 'web';
   expect(_ports, contains(root));
   var url = "http://localhost:${_ports[root]}";
   if (path != null) url = "$url/$path";
   return url;
 }