JS binding: remove redundant type check in attr setter for TypeChecking interface

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 bc4355c732fdd9107047fdd63c353c8f7f4ab40b..232cd24e0dfb9aeaec9c566364110dc3323100cb 100644
--- a/Source/bindings/scripts/v8_attributes.py
+++ b/Source/bindings/scripts/v8_attributes.py
@@ -323,6 +323,10 @@ def setter_context(interface, attribute, context):
          has_extended_attribute_value(attribute, 'TypeChecking', 'Interface')) and
         idl_type.is_wrapper_type)
 
+    type_checked = (has_type_checking_interface and
+                    # These allow null values, so a type-check is still required.
+                    not idl_type.is_nullable)
+
     context.update({
         'has_setter_exception_state':
             is_setter_raises_exception or has_type_checking_interface or
@@ -336,7 +340,8 @@ def setter_context(interface, attribute, context):
             'cppValue', isolate='scriptState->isolate()',
             creation_context='scriptState->context()->Global()'),
         'v8_value_to_local_cpp_value': idl_type.v8_value_to_local_cpp_value(
-            extended_attributes, 'v8Value', 'cppValue'),
+            extended_attributes, 'v8Value', 'cppValue',
+            needs_type_check=not type_checked),
     })
 
     # setter_expression() depends on context values we set above.