diff -r 000000000000 -r 6474c204b198 dom/bindings/CallbackInterface.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/bindings/CallbackInterface.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,33 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/CallbackInterface.h"
+#include "jsapi.h"
+#include "mozilla/dom/BindingUtils.h"
+#include "nsPrintfCString.h"
+
+namespace mozilla {
+namespace dom {
+
+bool
+CallbackInterface::GetCallableProperty(JSContext* cx, const char* aPropName,
+                                       JS::MutableHandle<JS::Value> aCallable)
+{
+  if (!JS_GetProperty(cx, CallbackPreserveColor(), aPropName, aCallable)) {
+    return false;
+  }
+  if (!aCallable.isObject() ||
+      !JS_ObjectIsCallable(cx, &aCallable.toObject())) {
+    nsPrintfCString description("Property '%s'", aPropName);
+    ThrowErrorMessage(cx, MSG_NOT_CALLABLE, description.get());
+    return false;
+  }
+
+  return true;
+}
+
+} // namespace dom
+} // namespace mozilla