Fix overloading for IDBDatabase transaction

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."""
 
 import emitter
 from generator import AnalyzeOperation, ConstantOutputOrder, \
@@ skipping 340 matching lines @@
 
       version[0] += 1
       generate_call(stmts_emitter, call_emitter,
           version[0], signature_index, argument_count)
 
     def GenerateChecksAndCall(signature_index, argument_count):
       checks = []
       for i in reversed(range(0, argument_count)):
         argument = signatures[signature_index][i]
         parameter_name = parameter_names[i]
-        test_type = self._DartType(argument.type.id)
+
+        test_type = self._NarrowToImplementationType(argument.type.id)
 
         if test_type in ['dynamic', 'Object']:
           checks.append('%s != null' % parameter_name)
         elif not can_omit_type_check(test_type, i):
           checks.append('(%s is %s || %s == null)' % (
               parameter_name, test_type, parameter_name))
         elif i >= number_of_required_in_dart:
           checks.append('%s != null' % parameter_name)
 
       # There can be multiple presence checks.  We need them all since a later
@@ skipping 374 matching lines @@
     # returned in generated code.
     assert(dart_name != 'HistoryBase' and dart_name != 'LocationBase')
     if dart_name == 'Window':
       return _secure_base_types[dart_name]
     return dart_name
 
   def SecureBaseName(self, type_name):
     if type_name in _secure_base_types:
       return _secure_base_types[type_name]
 
+  def _NarrowToImplementationType(self, type_name):
+    return self._type_registry.TypeInfo(type_name).narrow_dart_type()
+
+  def _NarrowInputType(self, type_name):
+    return self._NarrowToImplementationType(type_name)
+
   def _DartType(self, type_name):
     return self._type_registry.DartType(type_name)
 
   def _TypeInfo(self, type_name):
     return self._type_registry.TypeInfo(type_name)