Support WebIDL optional default value syntax

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 4cb00489c1f47da8882505ab320504f675e3ce1c..b4b0fca034075e95fcb02fb5d8de829d72e51e7f 100644
--- a/Source/bindings/scripts/v8_methods.py
+++ b/Source/bindings/scripts/v8_methods.py
@@ -145,6 +145,7 @@ def generate_argument(interface, method, argument, index):
     return {
         'cpp_type': idl_type.cpp_type_args(used_in_cpp_sequence=is_variadic_wrapper_type),
         'cpp_value': this_cpp_value,
+        'default_value': argument.default_value,
         'enum_validation_expression': idl_type.enum_validation_expression,
         'has_default': 'Default' in extended_attributes,
         'has_event_listener_argument': any(
@@ -194,8 +195,6 @@ def cpp_value(interface, method, number_of_arguments):
             return '%s.release()' % argument.name
         return argument.name
 
-    # Truncate omitted optional arguments
-    arguments = method.arguments[:number_of_arguments]
     cpp_arguments = v8_utilities.call_with_arguments(method)
     # Members of IDL partial interface definitions are implemented in C++ as
     # static member functions, which for instance members (non-static members)
@@ -203,7 +202,11 @@ def cpp_value(interface, method, number_of_arguments):
     if ('PartialInterfaceImplementedAs' in method.extended_attributes and
         not method.is_static):
         cpp_arguments.append('*impl')
-    cpp_arguments.extend(cpp_argument(argument) for argument in arguments)
+    cpp_arguments.extend(cpp_argument(argument)
+                         for argument in method.arguments[:number_of_arguments])
+    cpp_arguments.extend(argument.default_value
+                         for argument in method.arguments[number_of_arguments:]
+                         if argument.is_optional and argument.default_value)
     this_union_arguments = method.idl_type and method.idl_type.union_arguments
     if this_union_arguments:
         cpp_arguments.extend(this_union_arguments)