can't extend custom classes injected from C

src/gresource/js/ThemeUtils.js

@@ -30,7 +30,7 @@
 /**
  * Provides various utility methods and can be used by greeter themes if needed.
  */
-class ThemeUtils extends __ThemeUtils {
+class ThemeUtils  {
 	/**
 	 * Binds `this` to class, `context`, for all of the class's methods.
 	 *
@@ -38,7 +38,7 @@ class ThemeUtils extends __ThemeUtils {
 	 *
 	 * @return {function(new:*): Object} `context` with `this` bound to it for all of its methods.
 	 */
-	bind_this( context ) {
+	static bind_this( context ) {
 		let excluded_methods = ['constructor'];
 
 		function not_excluded( _method, _context ) {
@@ -63,7 +63,8 @@ class ThemeUtils extends __ThemeUtils {
 	}
 }
 
-window.theme_utils = new ThemeUtils();
+window.theme_utils = new __ThemeUtils();
+window.theme_utils.bind_this = ThemeUtils.bind_this;
 
 /* -------->>> DEPRECATED! <<<-------- */
 window.greeterutil = window.theme_utils;

src/webkit2-extension.c

@@ -1562,7 +1562,7 @@ static const JSClassDefinition config_file_definition = {
 
 static const JSClassDefinition theme_utils_definition = {
 	0,                                     /* Version          */
-	kJSClassAttributeNone,  /* Attributes       */
+	kJSClassAttributeNoAutomaticPrototype, /* Attributes       */
 	"__ThemeUtils",                        /* Class name       */
 	NULL,                                  /* Parent class     */
 	NULL,                                  /* Static values    */
@@ -1580,7 +1580,6 @@ window_object_cleared_callback(WebKitScriptWorld *world,
 	WebKitDOMDOMWindow *dom_window;
 	WebKitDOMDocument *dom_document;
 
-	JSStringRef command;
 	JSObjectRef gettext_object,
 				lightdm_greeter_object,
 				config_file_object,