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

ui/aura/window_tree_host_platform.cc

 // Copyright 2015 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_tree_host_platform.h"
 
 #include <utility>
 
 #include "base/trace_event/trace_event.h"
 #include "build/build_config.h"
 #include "ui/aura/window_event_dispatcher.h"
+#include "ui/aura/window_port.h"
 #include "ui/compositor/compositor.h"
 #include "ui/display/display.h"
 #include "ui/display/screen.h"
 #include "ui/events/event.h"
 
 #if defined(OS_ANDROID)
 #include "ui/platform_window/android/platform_window_android.h"
 #endif
 
 #if defined(USE_OZONE)
@@ skipping 23 matching lines @@
 #elif defined(OS_WIN)
   window_.reset(new ui::WinWindow(this, bounds));
 #elif defined(OS_ANDROID)
   window_.reset(new ui::PlatformWindowAndroid(this));
 #else
   NOTIMPLEMENTED();
 #endif
 }
 
 WindowTreeHostPlatform::WindowTreeHostPlatform()
-    : widget_(gfx::kNullAcceleratedWidget),
+    : WindowTreeHostPlatform(nullptr) {}
+
+WindowTreeHostPlatform::WindowTreeHostPlatform(
+    std::unique_ptr<WindowPort> window_port)
+    : WindowTreeHost(std::move(window_port)),
+      widget_(gfx::kNullAcceleratedWidget),
       current_cursor_(ui::kCursorNull) {
   CreateCompositor();
 }
 
 void WindowTreeHostPlatform::SetPlatformWindow(
     std::unique_ptr<ui::PlatformWindow> window) {
   window_ = std::move(window);
 }
 
 WindowTreeHostPlatform::~WindowTreeHostPlatform() {
@@ skipping 115 matching lines @@
   DCHECK_EQ(widget, widget_);
   widget_ = gfx::kNullAcceleratedWidget;
 }
 
 void WindowTreeHostPlatform::OnActivationChanged(bool active) {
   if (active)
     OnHostActivated();
 }
 
 }  // namespace aura