diff -r 000000000000 -r 6474c204b198 layout/base/nsIReflowCallback.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/base/nsIReflowCallback.h	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 -*- */
+/* 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/. */
+#ifndef nsIReflowCallback_h___
+#define nsIReflowCallback_h___
+
+/**
+ * Reflow callback interface.
+ * These are not refcounted. Objects must be removed from the presshell
+ * callback list before they die.
+ * Protocol: objects will either get a ReflowFinished() call when a reflow
+ * has finished or a ReflowCallbackCanceled() call if the shell is destroyed,
+ * whichever happens first. If the object is explicitly removed from the shell
+ * (using nsIPresShell::CancelReflowCallback()) before that occurs then neither
+ * of the callback methods are called.
+ */
+class nsIReflowCallback {
+public:
+  /**
+   * The presshell calls this when reflow has finished. Return true if
+   * you need a Flush_Layout to happen after this.
+   */
+  virtual bool ReflowFinished() = 0;
+  /**
+   * The presshell calls this on outstanding callback requests in its
+   * Destroy() method. The shell removes the request after calling
+   * ReflowCallbackCanceled().
+   */
+  virtual void ReflowCallbackCanceled() = 0;
+};
+
+#endif /* nsIReflowCallback_h___ */