IDL: Add missing type-check for callback function arguments

Source/bindings/templates/methods.cpp

 {##############################################################################}
 {% macro generate_method(method, world_suffix) %}
 {% filter conditional(method.conditional_string) %}
 static void {{method.name}}{{method.overload_index}}Method{{world_suffix}}(const v8::FunctionCallbackInfo<v8::Value>& info)
 {
     {# Local variables #}
     {% if method.has_exception_state %}
     ExceptionState exceptionState(ExceptionState::ExecutionContext, "{{method.name}}", "{{interface_name}}", info.Holder(), info.GetIsolate());
     {% endif %}
     {# Overloaded methods have length checked during overload resolution #}
@@ skipping 124 matching lines @@
 {% else %}{# argument.is_optional #}
 if (info.Length() <= {{argument.index}} || !{% if argument.is_nullable %}(info[{{argument.index}}]->IsFunction() || info[{{argument.index}}]->IsNull()){% else %}info[{{argument.index}}]->IsFunction(){% endif %}) {
     {{throw_type_error(method,
           '"The callback provided as parameter %s is not a function."' %
               (argument.index + 1)) | indent }}
     return;
 }
 {{argument.name}} = {% if argument.is_nullable %}info[{{argument.index}}]->IsNull() ? nullptr : {% endif %}V8{{argument.idl_type}}::create(v8::Local<v8::Function>::Cast(info[{{argument.index}}]), ScriptState::current(info.GetIsolate()));
 {% endif %}{# argument.is_optional #}
 {% endif %}{# argument.idl_type == 'EventListener' #}
+{% elif argument.is_callback_function %}
+if (!info[{{argument.index}}]->IsFunction(){% if argument.is_nullable %} && !info[{{argument.index}}]->IsNull(){% endif %}) {
+    {{throw_type_error(method,
+          '"The callback provided as parameter %s is not a function."' %
+              (argument.index + 1)) | indent(8)}}
+    return;
+}
+{{argument.v8_value_to_local_cpp_value}};
 {% elif argument.is_variadic_wrapper_type %}
 for (int i = {{argument.index}}; i < info.Length(); ++i) {
     if (!V8{{argument.idl_type}}::hasInstance(info[i], info.GetIsolate())) {
         {{throw_type_error(method, '"parameter %s is not of type \'%s\'."' %
                                    (argument.index + 1, argument.idl_type)) | indent(8)}}
         return;
     }
     {{argument.name}}.append(V8{{argument.idl_type}}::toImpl(v8::Local<v8::Object>::Cast(info[i])));
 }
 {% elif argument.is_dictionary %}
@@ skipping 497 matching lines @@
                               if method.overloads else
                               method.runtime_enabled_function) %}
     prototypeObject->Set(v8AtomicString(isolate, "{{method.name}}"), v8::FunctionTemplate::New(isolate, {{cpp_class_or_partial}}V8Internal::{{method.name}}MethodCallback, v8Undefined(), defaultSignature, {{method.number_of_required_arguments}})->GetFunction());
     {% endfilter %}{# runtime_enabled() #}
     {% endfilter %}{# exposed() #}
     {% endfilter %}{# per_context_enabled() #}
     {% endfor %}
     {% endif %}
 }
 {%- endmacro %}