Skip expensive hasInstance() type-checks in overloads

Source/bindings/scripts/v8_methods.py

Index: Source/bindings/scripts/v8_methods.py
diff --git a/Source/bindings/scripts/v8_methods.py b/Source/bindings/scripts/v8_methods.py
index 7d2b9f8c2d185e24f6ce5231ec40a29d1f35be9b..d6059e38bcc4c8fe28e8f4f29446ca7ffadc33d8 100644
--- a/Source/bindings/scripts/v8_methods.py
+++ b/Source/bindings/scripts/v8_methods.py
@@ -197,17 +197,22 @@ def argument_context(interface, method, argument, index):
          has_extended_attribute_value(method, 'TypeChecking', 'Interface')) and
         idl_type.is_wrapper_type)
 
-    type_checked = (type_checking_interface and
-                    # These allow null and undefined values, so a type-check is still required.
-                    not idl_type.is_nullable and
-                    not (argument.is_optional and
-                         'Default' in extended_attributes))
-
     if ('ImplementedInPrivateScript' in extended_attributes and
         not idl_type.is_wrapper_type and
         not idl_type.is_basic_type):
         raise Exception('Private scripts supports only primitive types and DOM wrappers.')
 
+    convert_v8_value_to_local_cpp_value = v8_value_to_local_cpp_value(
+        argument, index, return_promise=method.returns_promise)
+
+    # "Unsafe" conversion, to use when the argument's type has already been
+    # checked.  Set to None if same as regular conversion, to avoid emitting
+    # duplicate copies of the same code.
+    convert_v8_value_to_local_cpp_value_without_type_check = v8_value_to_local_cpp_value(
+        argument, index, needs_type_check=False, return_promise=method.returns_promise)
+    if convert_v8_value_to_local_cpp_value == convert_v8_value_to_local_cpp_value_without_type_check:
+        convert_v8_value_to_local_cpp_value_without_type_check = None
+
     default_cpp_value = argument.default_cpp_value
     return {
         'cpp_type': idl_type.cpp_type_args(extended_attributes=extended_attributes,
@@ -242,7 +247,8 @@ def argument_context(interface, method, argument, index):
             creation_context='scriptState->context()->Global()'),
         'v8_set_return_value': v8_set_return_value(interface.name, method, this_cpp_value),
         'v8_set_return_value_for_main_world': v8_set_return_value(interface.name, method, this_cpp_value, for_main_world=True),
-        'v8_value_to_local_cpp_value': v8_value_to_local_cpp_value(argument, index, type_checked, return_promise=method.returns_promise),
+        'v8_value_to_local_cpp_value': convert_v8_value_to_local_cpp_value,
+        'v8_value_to_local_cpp_value_without_type_check': convert_v8_value_to_local_cpp_value_without_type_check,
         'vector_type': v8_types.cpp_ptr_type('Vector', 'HeapVector', idl_type.gc_type),
     }
 
@@ -370,14 +376,15 @@ def v8_value_to_local_cpp_variadic_value(argument, index, return_promise):
     return '%s%s(%s)' % (macro, suffix, ', '.join(macro_args))
 
 
-def v8_value_to_local_cpp_value(argument, index, type_checked, return_promise=False):
+def v8_value_to_local_cpp_value(argument, index, needs_type_check=True, return_promise=False):
     extended_attributes = argument.extended_attributes
     idl_type = argument.idl_type
     name = argument.name
     if argument.is_variadic:
         return v8_value_to_local_cpp_variadic_value(argument, index, return_promise)
-    return idl_type.v8_value_to_local_cpp_value(extended_attributes, 'info[%s]' % index,
-                                                name, needs_type_check=not type_checked, index=index, declare_variable=False, return_promise=return_promise)
+    return idl_type.v8_value_to_local_cpp_value(
+        extended_attributes, 'info[%s]' % index, name, needs_type_check=needs_type_check,
+        index=index, declare_variable=False, return_promise=return_promise)
 
 
 ################################################################################