Rip out the last dart:io dependency from pkg/http.

pkg/http/test/html/utils.dart

Index: pkg/http/test/html/utils.dart
diff --git a/pkg/http/test/html/utils.dart b/pkg/http/test/html/utils.dart
new file mode 100644
index 0000000000000000000000000000000000000000..5803ec29550796cad0850e1e23db3e8a5e3bb094
--- /dev/null
+++ b/pkg/http/test/html/utils.dart
@@ -0,0 +1,19 @@
+// 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 http.test.html_utils;
+
+import 'dart:async';
+import 'dart:convert';
+import 'dart:html';
+
+import 'package:http/http.dart';
+import 'package:http/src/utils.dart';
+import 'package:unittest/unittest.dart';
+
+export '../utils.dart';
+
+/// The test server's echo URL.
+Uri get echoUrl => Uri.parse(
+    '${window.location.protocol}//${window.location.host}/echo');