Updating dwc for breaking changes that will be part of the next sdk

lib/src/file_system/browser.dart

 // Copyright (c) 2012, 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 browser;
 
 import 'dart:math';
 import 'dart:html';
 import 'path.dart';
-import 'package:web_components/src/file_system.dart';
+import 'package:web_components/src/file_system.dart' as fs;
 import 'package:js/js.dart' as js;
 
 /**
  * File system implementation indirectly using the Chrome Extension Api's to
  * proxy arbitrary urls. See extension/background.js for the code that does
  * the actual proxying.
  */
-class BrowserFileSystem implements FileSystem {
+class BrowserFileSystem implements fs.FileSystem {
 
   /**
    * Chrome extension port used to communicate back to the source page that
    * will consume these proxied urls.
    */
   js.Proxy sourcePagePort;
 
   final _filesToProxy = <String>{};
   final _random = new Random();
   final _uriScheme;
@@ skipping 27 matching lines @@
     var completer = new Completer<String>();
     // We must add a random id or a timestamp to defeat proxy servers and Chrome
     // caching when accessing file urls.
     var uniqueUrl = '$_uriScheme://$path?random_id=${_random.nextDouble()}';
     new HttpRequest.get(uniqueUrl, onSuccess(HttpRequest request) {
       completer.complete(request.responseText);
     });
     return completer.future;
   }
 }