Properly generate MutationCallback in dart:html.

lib/dom/scripts/dartgenerator.py

Index: lib/dom/scripts/dartgenerator.py
diff --git a/lib/dom/scripts/dartgenerator.py b/lib/dom/scripts/dartgenerator.py
index 713c534927f322cf3552c4d0891c1bb4988dfc13..4d089887c4e7210a9d8c3534e2b0e28cb516204d 100755
--- a/lib/dom/scripts/dartgenerator.py
+++ b/lib/dom/scripts/dartgenerator.py
@@ -35,14 +35,17 @@ class DartGenerator(object):
     return type_name.split('::')[-1]
 
   def _IsCompoundType(self, database, type_name):
-    if IsPrimitiveType(type_name):
+    if IsRegisteredType(type_name):
       return True
 
+    if type_name.endswith('?'):
+      return self._IsCompoundType(database, type_name[:-len('?')])
+
     if type_name.endswith('[]'):
       return self._IsCompoundType(database, type_name[:-len('[]')])
 
-    striped_type_name = self._StripModules(type_name)
-    if database.HasInterface(striped_type_name):
+    stripped_type_name = self._StripModules(type_name)
+    if database.HasInterface(stripped_type_name):
       return True
 
     dart_template_match = self._dart_templates_re.match(type_name)