Implementing polyfills for insertAdjacent* to get them working on FF.

lib/dom/scripts/systemhtml.py

 #!/usr/bin/python
 # 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.
 
 """This module provides shared functionality for the system to generate
 Dart:html APIs from the IDL database."""
 
 import emitter
 
 from systemdart2js import *
 from systeminterface import *
 
 _js_custom_members = set([
+    'Element.insertAdjacentElement',
+    'Element.insertAdjacentHTML',
+    'Element.insertAdjacentText',
     'IDBDatabase.transaction',
     'IFrameElement.contentWindow',
     'MouseEvent.offsetX',
     'MouseEvent.offsetY',
     'Window.document',
     'Window.top',
     'Window.location',
     'Window.open',
     ])
 
@@ skipping 1202 matching lines @@
     return HtmlDart2JSClassGenerator(self, interface)
 
   def GenerateLibraries(self, dart_files):
     self._GenerateLibFile(
         'html_dart2js.darttemplate',
         os.path.join(self._output_dir, 'html_dart2js.dart'),
         dart_files)
 
   def Finish(self):
     pass