diff -r 000000000000 -r 6474c204b198 xpcom/string/src/nsTPromiseFlatString.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/string/src/nsTPromiseFlatString.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,21 @@
+/* -*- 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/. */
+
+void
+nsTPromiseFlatString_CharT::Init(const substring_type& str)
+  {
+    if (str.IsTerminated())
+      {
+        mData = const_cast<char_type*>(static_cast<const char_type*>(str.Data()));
+        mLength = str.Length();
+        mFlags = str.mFlags & (F_TERMINATED | F_LITERAL);
+                 // does not promote F_VOIDED
+      }
+    else
+      {
+        Assign(str);
+      }
+  }