IDL: Add support for [Unscopeable] on attributes and methods

Source/bindings/templates/partial_interface.cpp

 {% extends 'interface_base.cpp' %}
 
+
+{##############################################################################}
+{% block prepare_prototype_object %}
+{% from 'interface.cpp' import install_unscopeables with context %}
+{% from 'methods.cpp' import install_conditionally_enabled_methods
+        with context %}
+void {{v8_class_or_partial}}::preparePrototypeObject(v8::Isolate* isolate, v8::Local<v8::Object> prototypeObject)
+{
+    {{v8_class}}::preparePrototypeObject(isolate, prototypeObject);
+{% if unscopeables %}
+    {{install_unscopeables() | indent}}
+{% endif %}
+{% if conditionally_enabled_methods %}
+    {{install_conditionally_enabled_methods() | indent}}
+{% endif %}
+}
+
+{% endblock %}
+
+
 {##############################################################################}
 {% block partial_interface %}
 void {{v8_class_or_partial}}::initialize()
 {
     // Should be invoked from initModules.
     {{v8_class}}::updateWrapperTypeInfo(
         &{{v8_class_or_partial}}::install{{v8_class}}Template,
-        &{{v8_class_or_partial}}::installConditionallyEnabledMethods);
+        &{{v8_class_or_partial}}::preparePrototypeObject);
     {% for method in methods %}
     {% if method.overloads and method.overloads.has_partial_overloads %}
     {{v8_class}}::register{{method.name | blink_capitalize}}MethodForPartialInterface(&{{cpp_class_or_partial}}V8Internal::{{method.name}}Method);
     {% endif %}
     {% endfor %}
 }
 
 {% endblock %}