IDL: Add [LegacyInterfaceTypeChecking] extended attribute

Source/bindings/scripts/v8_attributes.py

Index: Source/bindings/scripts/v8_attributes.py
diff --git a/Source/bindings/scripts/v8_attributes.py b/Source/bindings/scripts/v8_attributes.py
index 078b64c7f2e103a427727eb0596a01f358254ccb..e7042c836d614d26faaee453a8fe5e0c2c21dd3d 100644
--- a/Source/bindings/scripts/v8_attributes.py
+++ b/Source/bindings/scripts/v8_attributes.py
@@ -40,7 +40,8 @@ import v8_types
 import v8_utilities
 from v8_utilities import (cpp_name_or_partial, capitalize, cpp_name, has_extended_attribute,
                           has_extended_attribute_value, scoped_name, strip_suffix,
-                          uncapitalize, extended_attribute_value_as_list, is_unforgeable)
+                          uncapitalize, extended_attribute_value_as_list, is_unforgeable,
+                          is_legacy_interface_type_checking)
 
 
 def attribute_context(interface, attribute):
@@ -317,10 +318,9 @@ def setter_context(interface, attribute, context):
     is_setter_raises_exception = (
         'RaisesException' in extended_attributes and
         extended_attributes['RaisesException'] in [None, 'Setter'])
-    # [TypeChecking=Interface]
+    # [TypeChecking=Interface] / [LegacyInterfaceTypeChecking]
     has_type_checking_interface = (
-        (has_extended_attribute_value(interface, 'TypeChecking', 'Interface') or
-         has_extended_attribute_value(attribute, 'TypeChecking', 'Interface')) and
+        not is_legacy_interface_type_checking(interface, attribute) and
         idl_type.is_wrapper_type)
 
     context.update({