Add property to CssStyleDeclaration to detect if a CSS value is available.

tools/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
 import logging
@@ skipping 35 matching lines @@
     'ConsoleBase.profile',
     'ConsoleBase.profileEnd',
     'ConsoleBase.table',
     'ConsoleBase.time',
     'ConsoleBase.timeEnd',
     'ConsoleBase.timeStamp',
     'ConsoleBase.trace',
     'ConsoleBase.warn',
     'WebKitCSSKeyframesRule.insertRule',
     'CSSStyleDeclaration.setProperty',
+    'CSSStyleDeclaration.__propertyQuery__',
     'Document.createNodeIterator',
     'Document.createTreeWalker',
     'DOMException.name',
     'Element.createShadowRoot',
     'Element.insertAdjacentElement',
     'Element.insertAdjacentHTML',
     'Element.insertAdjacentText',
     'Element.remove',
     'Element.shadowRoot',
     'Element.matches',
@@ skipping 1200 matching lines @@
 
   def AddFile(self, basename, library_name, path):
     self._libraries[library_name].AddFile(path)
 
   def AddTypeEntry(self, library_name, idl_name, dart_name):
     self._libraries[library_name].AddTypeEntry(idl_name, dart_name)
 
   def Emit(self, emitter, auxiliary_dir):
     for lib in self._libraries.values():
       lib.Emit(emitter, auxiliary_dir)