IDL: Support using nullable on any method return type

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 234 matching lines @@
 {% endif %}
 {# Call #}
 {% if method.idl_type == 'void' %}
 {{cpp_value}};
 {% elif method.is_implemented_in_private_script %}
 {{method.cpp_type}} result;
 if (!{{method.cpp_value}})
     return;
 {% elif method.is_constructor %}
 {{method.cpp_type}} impl = {{cpp_value}};
-{% elif method.is_call_with_script_state or method.is_raises_exception %}
-{# FIXME: consider always using a local variable #}
+{% elif method.use_local_result and not method.union_arguments %}
 {{method.cpp_type}} result = {{cpp_value}};
 {% endif %}
 {# Post-call #}
 {% if method.is_raises_exception %}
 if (exceptionState.hadException()) {
     {{throw_from_exception_state(method)}};
     return;
 }
 {% endif %}
 {# Set return value #}
 {% if method.is_constructor %}
 {{generate_constructor_wrapper(method)}}
 {%- elif method.union_arguments %}
 {{union_type_method_call_and_set_return_value(method)}}
 {%- elif v8_set_return_value %}
+{% if method.is_nullable %}
+if (result.isNull())
+    v8SetReturnValueNull(info);
+else
+    {{v8_set_return_value}};
+{% else %}
 {{v8_set_return_value}};
+{% endif %}
 {%- endif %}{# None for void #}
 {# Post-set #}
 {% if interface_name == 'EventTarget' and method.name in ('addEventListener',
                                                           'removeEventListener') %}
 {% set hidden_dependency_action = 'addHiddenValueToArray'
        if method.name == 'addEventListener' else 'removeHiddenValueFromArray' %}
 {# Length check needed to skip action on legacy calls without enough arguments.
    http://crbug.com/353484 #}
 if (info.Length() >= 2 && listener && !impl->toNode())
     {{hidden_dependency_action}}(info.Holder(), info[1], {{v8_class}}::eventListenerCacheIndex, info.GetIsolate());
@@ skipping 302 matching lines @@
 v8::Handle<v8::Object> wrapper = wrap(impl.get(), info.Holder(), isolate);
 {% else %}
 {% set constructor_class = v8_class + ('Constructor'
                                        if constructor.is_named_constructor else
                                        '') %}
 v8::Handle<v8::Object> wrapper = info.Holder();
 V8DOMWrapper::associateObjectWithWrapper<{{v8_class}}>(impl.release(), &{{constructor_class}}::wrapperTypeInfo, wrapper, isolate, {{wrapper_configuration}});
 {% endif %}
 v8SetReturnValue(info, wrapper);
 {% endmacro %}