bindings: Supports [SameObject] extended attribute.

third_party/WebKit/Source/bindings/templates/attributes.cpp

 {% from 'utilities.cpp' import declare_enum_validation_variable, v8_value_to_local_cpp_value, check_origin_trial %}
 
 {##############################################################################}
 {% macro attribute_getter(attribute, world_suffix) %}
 static void {{attribute.name}}AttributeGetter{{world_suffix}}(
 {%- if attribute.is_data_type_property %}
 const v8::PropertyCallbackInfo<v8::Value>& info
 {%- else %}
 const v8::FunctionCallbackInfo<v8::Value>& info
 {%- endif %})
 {
     {% if attribute.origin_trial_enabled_function %}
     {{check_origin_trial(attribute) | indent}}
     {% endif %}
     {% if attribute.is_reflect and not attribute.is_url
           and attribute.idl_type == 'DOMString' and is_node
           and not attribute.is_implemented_in_private_script %}
     {% set cpp_class, v8_class = 'Element', 'V8Element' %}
     {% endif %}
     {# holder #}
     {% if not attribute.is_static %}
     {% if attribute.is_lenient_this %}
     {# Make sure that info.Holder() really points to an instance if [LenientThis]. #}
     if (!{{v8_class}}::hasInstance(info.Holder(), info.GetIsolate()))
         return; // Return silently because of [LenientThis].
     {% endif %}
     v8::Local<v8::Object> holder = info.Holder();
     {% endif %}
     {# impl #}
+    {% if not attribute.is_static %}
+    {{cpp_class}}* impl = {{v8_class}}::toImpl(holder);
+    {% endif %}
+    {% if attribute.is_same_object %}
+    v8::Local<v8::String> propertyName = v8AtomicString(info.GetIsolate(), "sameobject_{{attribute.name}}");
+    {
+        v8::Local<v8::Value> v8Value = V8HiddenValue::getHiddenValue(ScriptState::current(info.GetIsolate()), holder, propertyName);
+        if (!v8Value.IsEmpty()) {
+            v8SetReturnValue(info, v8Value);
+            return;
+        }
+    }
+    {% endif %}
     {% if attribute.cached_attribute_validation_method %}
     v8::Local<v8::String> propertyName = v8AtomicString(info.GetIsolate(), "{{attribute.name}}");
-    {{cpp_class}}* impl = {{v8_class}}::toImpl(holder);
     if (!impl->{{attribute.cached_attribute_validation_method}}()) {
         v8::Local<v8::Value> v8Value = V8HiddenValue::getHiddenValue(ScriptState::current(info.GetIsolate()), holder, propertyName);
         if (!v8Value.IsEmpty() && !v8Value->IsUndefined()) {
             v8SetReturnValue(info, v8Value);
             return;
         }
     }
-    {% elif not attribute.is_static %}
-    {{cpp_class}}* impl = {{v8_class}}::toImpl(holder);
     {% endif %}
     {% if interface_name == 'Window' and attribute.idl_type == 'EventHandler' %}
     if (!impl->document())
         return;
     {% endif %}
     {# Local variables #}
     {% if attribute.is_call_with_execution_context %}
     ExecutionContext* executionContext = currentExecutionContext(info.GetIsolate());
     {% endif %}
     {% if attribute.is_call_with_script_state %}
@@ skipping 64 matching lines @@
     }
     {% 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 %}
+    {% if attribute.is_same_object %}
+    V8HiddenValue::setHiddenValue(ScriptState::current(info.GetIsolate()), holder, propertyName, info.GetReturnValue().Get());

[haraken, 2016/05/16 09:17:44]

Can we merge the branch with '{% if attribute.cached_attribute_validation_method
%}' ?

[Yuki, 2016/05/16 09:32:14]

I had the same idea, but it turned out that it's not so easy or it doesn't make
the code cleaner.

The underlying difficulty is that
- the resulting value is sometimes stored in |v8Value|, but not always.
- since we're relying on attr.v8_set_return_value, we don't know exactly where
the return value is stored.  If it's not |v8Value|, where?
- v8SetReturnValueString, v8SetReturnValue and v8SetReturnValueFast take a
different number of arguments.

Sigh...

+    {% endif %}
 }
 {% 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
    one of those. If not, set it to the empty string.
    http://www.whatwg.org/specs/web-apps/current-work/#limited-to-only-known-values #}
@@ skipping 363 matching lines @@
        setter_callback_for_main_world,
        wrapper_type_info,
        access_control,
        property_attribute,
        only_exposed_to_private_script,
        property_location(attribute),
        holder_check,
    ] %}
 {{'{'}}{{attribute_configuration_list | join(', ')}}{{'}'}}
 {%- endmacro %}