diff -r 000000000000 -r 6474c204b198 widget/xpwidgets/nsAppShellSingleton.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/widget/xpwidgets/nsAppShellSingleton.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,88 @@
+/* -*- Mode: c++; tab-width: 2; indent-tabs-mode: nil; -*- */
+/* 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 nsAppShellSingleton_h__
+#define nsAppShellSingleton_h__
+
+/**
+ * This file is designed to be included into the file that provides the
+ * nsIModule implementation for a particular widget toolkit.
+ *
+ * The following functions are defined:
+ *   nsAppShellInit
+ *   nsAppShellShutdown
+ *   nsAppShellConstructor
+ *
+ * The nsAppShellInit function is designed to be used as a module constructor.
+ * If you already have a module constructor, then call nsAppShellInit from your
+ * module constructor.
+ *
+ * The nsAppShellShutdown function is designed to be used as a module
+ * destructor.  If you already have a module destructor, then call
+ * nsAppShellShutdown from your module destructor.
+ *
+ * The nsAppShellConstructor function is designed to be used as a factory
+ * method for the nsAppShell class.
+ */
+
+#include "nsXULAppAPI.h"
+#if defined(MOZ_METRO) && defined(XP_WIN)
+#include "winrt/MetroAppShell.h"
+#endif
+
+static nsIAppShell *sAppShell;
+
+static nsresult
+nsAppShellInit()
+{
+  NS_ASSERTION(!sAppShell, "already initialized");
+
+#if !defined(MOZ_METRO) || !defined(XP_WIN)
+  sAppShell = new nsAppShell();
+#else
+  if (XRE_GetWindowsEnvironment() == WindowsEnvironmentType_Metro) {
+    sAppShell = new MetroAppShell();
+  } else {
+    sAppShell = new nsAppShell();
+  }
+#endif
+  if (!sAppShell)
+    return NS_ERROR_OUT_OF_MEMORY;
+  NS_ADDREF(sAppShell);
+
+  nsresult rv;
+#if !defined(MOZ_METRO) || !defined(XP_WIN)
+  rv = static_cast<nsAppShell*>(sAppShell)->Init();
+#else
+  if (XRE_GetWindowsEnvironment() == WindowsEnvironmentType_Metro) {
+    rv = static_cast<MetroAppShell*>(sAppShell)->Init();
+  } else {
+    rv = static_cast<nsAppShell*>(sAppShell)->Init();
+  }
+#endif
+  if (NS_FAILED(rv)) {
+    NS_RELEASE(sAppShell);
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+static void
+nsAppShellShutdown()
+{
+  NS_RELEASE(sAppShell);
+}
+
+static nsresult
+nsAppShellConstructor(nsISupports *outer, const nsIID &iid, void **result)
+{
+  NS_ENSURE_TRUE(!outer, NS_ERROR_NO_AGGREGATION);
+  NS_ENSURE_TRUE(sAppShell, NS_ERROR_NOT_INITIALIZED);
+
+  return sAppShell->QueryInterface(iid, result);
+}
+
+#endif  // nsAppShellSingleton_h__