Adds a porting layer so aura can be made to work with mus

ui/aura/window_port.cc

+// 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.
+
+#include "ui/aura/window_port.h"
+
+#include "ui/aura/window.h"
+
+namespace aura {
+
+// static
+WindowPort* WindowPort::Get(Window* window) {
+  return window ? window->port_ : nullptr;
+}
+
+// static
+base::ObserverList<WindowObserver, true>* WindowPort::GetObservers(
+    Window* window) {
+  return &(window->observers_);
+}
+
+}  // namespace aura