Added tests to previously broken functionality and added null checks.

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 222 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 range(0, argument_count):
         argument = signatures[signature_index][i]
         parameter_name = parameter_names[i]
         test_type = self._DartType(argument.type.id)
+        nullable = False or argument.type.nullable
+
         if test_type in ['dynamic', 'Object']:
           checks.append('?%s' % parameter_name)
         elif not can_omit_type_check(test_type, i):
+          nullable = True
           checks.append('(%s is %s || %s == null)' % (
               parameter_name, test_type, parameter_name))
+
+        if not nullable:
+          for signature in signatures:
+            if (len(signature) <= i or signature[i] != argument):
+              checks.append('%s != null' % parameter_name)
+              break
+
       # There can be multiple presence checks.  We need them all since a later
       # optional argument could have been passed by name, leaving 'holes'.
       checks.extend(['!?%s' % name for name in parameter_names[argument_count:]])
 
       GenerateCall(signature_index, argument_count, checks)
 
     # TODO: Optimize the dispatch to avoid repeated checks.
     if len(signatures) > 1:
       index_swaps = {}
       for signature_index, signature in enumerate(signatures):
@@ skipping 322 matching lines @@
     if interface.parents:
       parent = interface.parents[0]
       if IsPureInterface(parent.type.id):
         walk(interface.parents)
       else:
         walk(interface.parents[1:])
     return result
 
   def _DartType(self, type_name):
     return self._type_registry.DartType(type_name)