IDL: Generate union type containers

Source/bindings/scripts/v8_interface.py

Index: Source/bindings/scripts/v8_interface.py
diff --git a/Source/bindings/scripts/v8_interface.py b/Source/bindings/scripts/v8_interface.py
index 889dc5bd48a9222255d57a97d20ae8cc0cab1746..2e2a385ad544edd769669e984a77495304b4d09f 100644
--- a/Source/bindings/scripts/v8_interface.py
+++ b/Source/bindings/scripts/v8_interface.py
@@ -1045,10 +1045,7 @@ def interface_length(interface, constructors):
 def property_getter(getter, cpp_arguments):
     def is_null_expression(idl_type):
         if idl_type.is_union_type:
-            notnull = ' || '.join([
-                    member_argument['null_check_value']
-                    for member_argument in idl_type.union_arguments])
-            return '!(%s)' % notnull
+            return 'result.isNull()'
         if idl_type.name == 'String':
             return 'result.isNull()'
         if idl_type.is_interface_type:
@@ -1064,10 +1061,9 @@ def property_getter(getter, cpp_arguments):
 
     if is_raises_exception:
         cpp_arguments.append('exceptionState')
-    union_arguments = idl_type.union_arguments
-    if union_arguments:
-        cpp_arguments.extend([member_argument['cpp_value']
-                              for member_argument in union_arguments])
+    union_result_members = idl_type.union_result_members
+    if union_result_members:
+        cpp_arguments.append('result')
 
     cpp_value = '%s(%s)' % (cpp_method_name, ', '.join(cpp_arguments))
 
@@ -1086,7 +1082,7 @@ def property_getter(getter, cpp_arguments):
         'is_null_expression': is_null_expression(idl_type),
         'is_raises_exception': is_raises_exception,
         'name': cpp_name(getter),
-        'union_arguments': union_arguments,
+        'union_result_members': union_result_members,
         'v8_set_return_value': idl_type.v8_set_return_value('result', extended_attributes=extended_attributes, script_wrappable='impl', release=idl_type.release),
     }