aura: Use PlatformWindow from WindowTreeHost.

ui/aura/window_tree_host_ozone.cc

 // Copyright 2013 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_ozone.h"
 
 #include "ui/aura/window_event_dispatcher.h"
 #include "ui/ozone/public/cursor_factory_ozone.h"
 #include "ui/ozone/public/event_factory_ozone.h"
 #include "ui/ozone/public/ozone_platform.h"
@@ skipping 38 matching lines @@
 
 void WindowTreeHostOzone::OnLostCapture() {
 }
 
 void WindowTreeHostOzone::OnAcceleratedWidgetAvailable(
     gfx::AcceleratedWidget widget) {
   widget_ = widget;
   CreateCompositor(widget_);
 }
 
+void WindowTreeHostOzone::OnActivationChanged(bool active) {
+}
+
 ui::EventSource* WindowTreeHostOzone::GetEventSource() {
   return this;
 }
 
 gfx::AcceleratedWidget WindowTreeHostOzone::GetAcceleratedWidget() {
   return widget_;
 }
 
 void WindowTreeHostOzone::Show() {
   platform_window_->Show();
@@ skipping 51 matching lines @@
   return new WindowTreeHostOzone(bounds);
 }
 
 // static
 gfx::Size WindowTreeHost::GetNativeScreenSize() {
   NOTIMPLEMENTED();
   return gfx::Size();
 }
 
 }  // namespace aura