import FIREFOX_52_6_0esr_RELEASE from mozilla-esr52 hg repo

layout/style/StyleBackendType.h

@@ -0,0 +1,23 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 mozilla_StyleBackendType_h
+#define mozilla_StyleBackendType_h
+
+namespace mozilla {
+
+/**
+ * Enumeration that represents one of the two supported style system backends.
+ */
+enum class StyleBackendType : uint8_t
+{
+  Gecko = 1,
+  Servo
+};
+
+} // namespace mozilla
+
+#endif // mozilla_StyleBackendType_h