Add PlatformWindow/Event related code for Ozone X11.

ui/ozone/platform/x11/ozone_platform_x11.h

Index: ui/ozone/platform/x11/ozone_platform_x11.h
diff --git a/ui/ozone/platform/x11/ozone_platform_x11.h b/ui/ozone/platform/x11/ozone_platform_x11.h
new file mode 100644
index 0000000000000000000000000000000000000000..b1f28a4fc7e971be44eb694bdf788d71e87de74a
--- /dev/null
+++ b/ui/ozone/platform/x11/ozone_platform_x11.h
@@ -0,0 +1,17 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_OZONE_PLATFORM_X11_OZONE_PLATFORM_X11_H_
+#define UI_OZONE_PLATFORM_X11_OZONE_PLATFORM_X11_H_
+
+namespace ui {
+
+class OzonePlatform;
+
+// Constructor hook for use in ozone_platform_list.cc
+OzonePlatform* CreateOzonePlatformX11();
+
+}  // namespace ui
+
+#endif  // UI_OZONE_PLATFORM_X11_OZONE_PLATFORM_X11_H_