Don't use file-based part-of when part files are shared.

sdk/lib/html/html_common/device.dart

 // Copyright (c) 2011, 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.
 
-part of "html_common.dart";
+part of html_common;
 
 /**
  * Utils for device detection.
  */
 class Device {
   static bool _isOpera;
   static bool _isIE;
   static bool _isFirefox;
   static bool _isWebKit;
   static String _cachedCssPrefix;
@@ skipping 87 matching lines @@
    */
   static bool isEventTypeSupported(String eventType) {
     // Browsers throw for unsupported event names.
     try {
       var e = new Event.eventType(eventType, '');
       return e is Event;
     } catch (_) {}
     return false;
   }
 }