diff -r 000000000000 -r 6474c204b198 xpcom/base/nsIMessageLoop.idl
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/base/nsIMessageLoop.idl	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,36 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 "nsISupports.idl"
+
+interface nsIRunnable;
+
+/**
+ * This service allows access to the current thread's Chromium MessageLoop
+ * instance, with some extra sugar added.  If you're calling from C++, it may
+ * or may not make sense for you to use this interface.  If you're calling from
+ * JS, you don't have a choice!
+ *
+ * Right now, you can only call PostIdleTask(), but nothing is stopping you
+ * from adding other methods.
+ *
+ * nsIMessageLoop's contractid is "@mozilla.org/message-loop;1".
+ */
+[scriptable, uuid(3E8C58E8-E52C-43E0-8E66-669CA788FF5F)]
+interface nsIMessageLoop : nsISupports
+{
+  /**
+   * Posts a task to be run when this thread's message loop is idle, or after
+   * ensureRunsAfterMS milliseconds have elapsed.  (That is, the task is
+   * guaranteed to run /eventually/.)
+   *
+   * Note that if the event loop is busy, we will hold a reference to the task
+   * until ensureRunsAfterMS milliseconds have elapsed.  Be careful when
+   * specifying long timeouts and tasks which hold references to windows or
+   * other large objects, because you can leak memory in a difficult-to-detect
+   * way!
+   */
+  void postIdleTask(in nsIRunnable task, in uint32_t ensureRunsAfterMS);
+};