IDL: Union type support for attributes

Source/bindings/templates/attributes.cpp

 {##############################################################################}
 {% macro attribute_getter(attribute, world_suffix) %}
 {% filter conditional(attribute.conditional_string) %}
 static void {{attribute.name}}AttributeGetter{{world_suffix}}(
 {%- if attribute.is_expose_js_accessors %}
 const v8::FunctionCallbackInfo<v8::Value>& info
 {%- else %}
 const v8::PropertyCallbackInfo<v8::Value>& info
 {%- endif %})
 {
@@ skipping 77 matching lines @@
     if ({{attribute.cpp_value}} && DOMDataStore::setReturnValueFromWrapper{{world_suffix}}<V8{{attribute.idl_type}}>(info.GetReturnValue(), {{attribute.cpp_value}}.get()))
         return;
     v8::Handle<v8::Value> wrapper = toV8({{attribute.cpp_value}}.get(), holder, info.GetIsolate());
     if (!wrapper.IsEmpty()) {
         V8HiddenValue::setHiddenValue(info.GetIsolate(), holder, v8AtomicString(info.GetIsolate(), "{{attribute.name}}"), wrapper);
         {{attribute.v8_set_return_value}};
     }
     {% elif world_suffix %}
     {{attribute.v8_set_return_value_for_main_world}};
     {% else %}
+    {% if attribute.use_output_parameter_for_result %}
+    {{attribute.cpp_type}} result;
+    {{attribute.cpp_value}};
+    {% endif %}
     {{attribute.v8_set_return_value}};
     {% endif %}
 }
 {% endfilter %}
 {% endmacro %}
 
 {######################################}
 {% macro release_only_check(reflect_only_values, reflect_missing,
                             reflect_invalid, reflect_empty, cpp_value) %}
 {# Attribute is limited to only known values: check that the attribute value is
@@ skipping 108 matching lines @@
     {# Type checking #}
     {% if attribute.has_type_checking_interface %}
     {# Type checking for interface types (if interface not implemented, throw
        TypeError), per http://www.w3.org/TR/WebIDL/#es-interface #}
     if ({% if attribute.is_nullable %}!isUndefinedOrNull(v8Value) && {% endif %}!V8{{attribute.idl_type}}::hasInstance(v8Value, info.GetIsolate())) {
         exceptionState.throwTypeError("The provided value is not of type '{{attribute.idl_type}}'.");
         exceptionState.throwIfNeeded();
         return;
     }
     {% endif %}
+    {% if attribute.use_output_parameter_for_result %}
+    {{attribute.cpp_type}} cppValue;
+    {% endif %}
     {# impl #}
     {% if attribute.put_forwards %}
     {{cpp_class}}* proxyImpl = {{v8_class}}::toImpl(holder);
     {{attribute.cpp_type}} impl = WTF::getPtr(proxyImpl->{{attribute.name}}());
     if (!impl)
         return;
     {% elif not attribute.is_static %}
     {{cpp_class}}* impl = {{v8_class}}::toImpl(holder);
     {% endif %}
     {% if attribute.idl_type == 'EventHandler' and interface_name == 'Window' %}
@@ skipping 191 matching lines @@
        access_control,
        property_attribute,
        only_exposed_to_private_script,
    ] %}
 {% if not attribute.is_expose_js_accessors %}
 {% set attribute_configuration_list = attribute_configuration_list
                                     + [on_prototype] %}
 {% endif %}
 {{'{'}}{{attribute_configuration_list | join(', ')}}{{'}'}}
 {%- endmacro %}