Add support in generate scripts to handle Conditional

Source/build/scripts/make_element_type_helpers.py

Index: Source/build/scripts/make_element_type_helpers.py
diff --git a/Source/build/scripts/make_element_type_helpers.py b/Source/build/scripts/make_element_type_helpers.py
index d92ade5d6e5c8851e81670e8fedf0e28b0977e0e..69817fc0839a9cfc2d7a2c5d6dfad6d114c21137 100755
--- a/Source/build/scripts/make_element_type_helpers.py
+++ b/Source/build/scripts/make_element_type_helpers.py
@@ -22,9 +22,7 @@ def _symbol(tag):
 
 class MakeElementTypeHelpersWriter(in_generator.Writer):
     defaults = {
-        'interfaceName': None,
-        'noConstructor': None,
-        'noTypeHelpers': None,
+        'Conditional': None,
         'ImplementedAs': None,
         'JSInterfaceName': None,
         'constructorNeedsCreatedByParser': None,
@@ -32,17 +30,20 @@ class MakeElementTypeHelpersWriter(in_generator.Writer):
         'contextConditional': None,
         'interfaceName': None,
         'noConstructor': None,
+        'noConstructor': None,
+        'noTypeHelpers': None,
         'runtimeEnabled': None,
     }
     default_parameters = {
         'attrsNullNamespace': None,
+        'fallbackInterfaceName': '',
         'namespace': '',
         'namespacePrefix': '',
         'namespaceURI': '',
-        'fallbackInterfaceName': '',
         'fallbackJSInterfaceName': '',
     }
     filters = {
+        'enable_conditional': name_utilities.enable_conditional_if_endif,
         'hash': hasher.hash,
         'symbol': _symbol,
     }