sky/shell should link with sky/engine

sky/shell/shell.h

 // 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.
 
 #ifndef SKY_SHELL_SHELL_H_
 #define SKY_SHELL_SHELL_H_
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "sky/shell/gpu/rasterizer.h"
 #include "sky/shell/sky_view.h"
+#include "sky/shell/ui/engine.h"
 
 namespace base {
 class Thread;
 class SingleThreadTaskRunner;
 }
 
 namespace sky {
 namespace shell {
 class SkyView;
 
 class Shell : public SkyView::Delegate {
  public:
   explicit Shell(scoped_refptr<base::SingleThreadTaskRunner> java_task_runner);
   ~Shell();
 
   void Init();
 
  private:
   void OnAcceleratedWidgetAvailable(gfx::AcceleratedWidget widget) override;
   void OnDestroyed() override;
 
   scoped_refptr<base::SingleThreadTaskRunner> java_task_runner_;
   scoped_ptr<base::Thread> gpu_thread_;
+  scoped_ptr<base::Thread> ui_thread_;
 
   scoped_ptr<SkyView> view_;
   scoped_ptr<Rasterizer> rasterizer_;
+  scoped_ptr<Engine> engine_;
 
   DISALLOW_COPY_AND_ASSIGN(Shell);
 };
 
 }  // namespace shell
 }  // namespace sky
 
 #endif  // SKY_SHELL_SHELL_H_