Fixed some bugs in dom docs and recovered documentation of Canvas stuff.

tools/dom/scripts/htmldartgenerator.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."""
 
 from generator import AnalyzeOperation, ConstantOutputOrder, \
     DartDomNameOfAttribute, FindMatchingAttribute, IsDartCollectionType, \
-    IsPureInterface, TypeOrNothing, FindCommonAnnotations
+    IsPureInterface, TypeOrNothing
 
 # Types that are accessible cross-frame in a limited fashion.
 # In these cases, the base type (e.g., WindowBase) provides restricted access
 # while the subtype (e.g., Window) provides full access to the
 # corresponding objects if there are from the same frame.
 _secure_base_types = {
   'Window': 'WindowBase',
   'Location': 'LocationBase',
   'History': 'HistoryBase',
 }
@@ skipping 451 matching lines @@
         walk(interface.parents)
       else:
         walk(interface.parents[1:])
     return result
 
   def _DartType(self, type_name):
     return self._type_registry.DartType(type_name)
 
   def _IsPrivate(self, name):
     return name.startswith('_')