Initial Dartium custom element support

tools/dom/templates/html/dartium/html_dartium.darttemplate

 // 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.
 
 // DO NOT EDIT
 // Auto-generated dart:html library.
 
 /// The Dart HTML library.
 ///
 /// For examples, see
 /// [Dart HTML5 Samples](https://github.com/dart-lang/dart-html5-samples)
 /// on Github.
 library dart.dom.html;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:_collection-dev' hide Symbol, deprecated;
 import 'dart:html_common';
 import 'dart:indexed_db';
 import 'dart:isolate';
 import 'dart:json' as json;
 import 'dart:math';
+// TODO(vsm): Remove this when we can do the proper checking in
+// native code for custom elements.
+import 'dart:mirrors';
 import 'dart:nativewrappers';
 import 'dart:typed_data';
 import 'dart:web_gl' as gl;
 import 'dart:web_sql';
 // Not actually used, but imported since dart:html can generate these objects.
 import 'dart:svg' as svg;
 import 'dart:web_audio' as web_audio;
 
 $!GENERATED_DART_FILES
 
@@ skipping 77 matching lines @@
       _callPortLastResult = json.parse(_getPortSyncEventData(event));
     });
     _callPortInitialized = true;
   }
   assert(_callPortLastResult == null);
   _dispatchEvent('js-sync-message', {'id': id, 'message': message});
   var result = _callPortLastResult;
   _callPortLastResult = null;
   return result;
 }