binding: Makes [SaveSameObject] use V8PrivateProperty.

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 %})
@@ skipping 10 matching lines @@
     {% 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 attribute.is_save_same_object %}
-    v8::Local<v8::String> propertyName = v8AtomicString(info.GetIsolate(), "sameobject_{{attribute.name}}");
+    {% set same_object_private_symbol = 'SameObject' + interface_name + attribute.name[0]|capitalize + attribute.name[1:] %}
+    // If you see a compile error that
+    //   V8PrivateProperty::get{{same_object_private_symbol}}
+    // is not defined, then you need to register your attribute at
+    // V8_PRIVATE_PROPERTY_FOR_EACH defined in V8PrivateProperty.h as
+    //   X(SameObject, {{interface_name}}{{attribute.name[0]|capitalize}}{{attribute.name[1:]}})
+    auto privateSameObject = V8PrivateProperty::getSameObject{{interface_name}}{{attribute.name[0]|capitalize}}{{attribute.name[1:]}}(info.GetIsolate());
     {
-        v8::Local<v8::Value> v8Value = V8HiddenValue::getHiddenValue(ScriptState::current(info.GetIsolate()), holder, propertyName);
+        v8::Local<v8::Value> v8Value = privateSameObject.get(info.GetIsolate()->GetCurrentContext(), holder);
         if (!v8Value.IsEmpty()) {
             v8SetReturnValue(info, v8Value);
             return;
         }
     }
     {% endif %}
     {% if not attribute.is_static %}
     {{cpp_class}}* impl = {{v8_class}}::toImpl(holder);
     {% endif %}
     {% if attribute.cached_attribute_validation_method %}
@@ skipping 83 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_save_same_object %}
-    V8HiddenValue::setHiddenValue(ScriptState::current(info.GetIsolate()), holder, propertyName, info.GetReturnValue().Get());
+    privateSameObject.set(info.GetIsolate()->GetCurrentContext(), holder, info.GetReturnValue().Get());
     {% 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.
@@ skipping 364 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 %}