Fix --pub-serve's path separator on Windows.

lib/src/runner/browser/server.dart

 // Copyright (c) 2015, 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.
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
 import 'package:async/async.dart';
 import 'package:http_multi_server/http_multi_server.dart';
@@ skipping 201 matching lines @@
         !new File(htmlPath).readAsStringSync()
             .contains('packages/test/dart.js')) {
       throw new LoadException(
           path,
           '"${htmlPath}" must contain <script src="packages/test/dart.js">'
               '</script>.');
     }
 
     var suiteUrl;
     if (_config.pubServeUrl != null) {
-      var suitePrefix = p.withoutExtension(
-          p.relative(path, from: p.join(_root, 'test')));
+      var suitePrefix = p.toUri(p.withoutExtension(
+          p.relative(path, from: p.join(_root, 'test')))).path;
 
       var dartUrl;
       // Polymer generates a bootstrap entrypoint that wraps the entrypoint we
       // see on disk, and modifies the HTML file to point to the bootstrap
       // instead. To make sure we get the right source maps and wait for the
       // right file to compile, we have some Polymer-specific logic here to load
       // the boostrap instead of the unwrapped file.
       if (isPolymerEntrypoint(path)) {
         dartUrl = _config.pubServeUrl.resolve(
             "$suitePrefix.html.polymer.bootstrap.dart.browser_test.dart");
@@ skipping 170 matching lines @@
       await Future.wait(futures);
 
       if (_config.pubServeUrl == null) {
         new Directory(_compiledDir).deleteSync(recursive: true);
       } else {
         _http.close();
       }
     });
   }
 }