diff -r 000000000000 -r 6474c204b198 xpcom/glue/MainThreadUtils.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/glue/MainThreadUtils.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,50 @@
+/* -*- 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/. */
+
+#ifndef MainThreadUtils_h_
+#define MainThreadUtils_h_
+
+#include "nscore.h"
+#include "mozilla/threads/nsThreadIDs.h"
+
+class nsIThread;
+
+/**
+ * Get a reference to the main thread.
+ *
+ * @param result
+ *   The resulting nsIThread object.
+ */
+extern NS_COM_GLUE NS_METHOD
+NS_GetMainThread(nsIThread **result);
+
+#if defined(MOZILLA_INTERNAL_API) && defined(XP_WIN)
+bool NS_IsMainThread();
+#elif defined(MOZILLA_INTERNAL_API) && defined(NS_TLS)
+// This is defined in nsThreadManager.cpp and initialized to `Main` for the
+// main thread by nsThreadManager::Init.
+extern NS_TLS mozilla::threads::ID gTLSThreadID;
+#ifdef MOZ_ASAN
+// Temporary workaround, see bug 895845
+MOZ_ASAN_BLACKLIST bool NS_IsMainThread();
+#else
+inline
+bool NS_IsMainThread()
+{
+  return gTLSThreadID == mozilla::threads::Main;
+}
+#endif
+#else
+/**
+ * Test to see if the current thread is the main thread.
+ *
+ * @returns true if the current thread is the main thread, and false
+ * otherwise.
+ */
+extern NS_COM_GLUE bool NS_IsMainThread();
+#endif
+
+#endif // MainThreadUtils_h_