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

pkg/http/test/html/client_test.dart

+// 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 client_test;
+
+import 'package:http/http.dart' as http;
+import 'package:http/browser_client.dart';
+import 'package:unittest/unittest.dart';
+
+import 'utils.dart';
+
+void main() {
+  test('#send a StreamedRequest', () {
+    var client = new BrowserClient();
+    var request = new http.StreamedRequest("POST", echoUrl);
+
+    expect(client.send(request).then((response) {
+      return response.stream.bytesToString();
+    }).whenComplete(client.close), completion(equals('{"hello": "world"}')));
+
+    request.sink.add('{"hello": "world"}'.codeUnits);
+    request.sink.close();
+  });
+
+  test('#send with an invalid URL', () {
+    var client = new BrowserClient();
+    var url = Uri.parse('http://http.invalid');
+    var request = new http.StreamedRequest("POST", url);
+
+    expect(client.send(request),
+        throwsClientException("XMLHttpRequest error."));
+
+    request.sink.add('{"hello": "world"}'.codeUnits);
+    request.sink.close();
+  });
+}