Start unification of overload dispatcher generation.

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, \
@@ skipping 175 matching lines @@
         # FIXME: item should be renamed to operator[], not removed.
         self.EmitOperation(info, '_item')
       return
 
     if declare_only:
       self.DeclareOperation(info,
           self.SecureOutputType(info.type_name), method_name)
     else:
       self.EmitOperation(info, method_name)
 
+  def _OverloadChecks(self,
+      operation,
+      parameter_names,
+      argument_count,
+      can_omit_type_check=lambda type, pos: False):
+    checks = []
+    for i in range(0, argument_count):
+      argument = operation.arguments[i]
+      parameter_name = parameter_names[i]
+      test_type = self._DartType(argument.type.id)
+      if test_type in ['dynamic', 'Object']:
+        checks.append('?%s' % parameter_name)
+      elif not can_omit_type_check(test_type, i):
+        checks.append('(%s is %s || %s == null)' % (
+            parameter_name, test_type, parameter_name))
+    # 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:]])
+    return checks
+
   def AdditionalImplementedInterfaces(self):
     # TODO: Include all implemented interfaces, including other Lists.
     implements = []
     if self._interface_type_info.is_typed_array():
       element_type = self._interface_type_info.list_item_type()
       implements.append('List<%s>' % self._DartType(element_type))
     if self._interface_type_info.list_item_type():
       item_type_info = self._type_registry.TypeInfo(
           self._interface_type_info.list_item_type())
       implements.append('List<%s>' % item_type_info.dart_type())
@@ skipping 213 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('_')