sky/shell should link with sky/engine

sky/shell/shell.h

Index: sky/shell/shell.h
diff --git a/sky/shell/shell.h b/sky/shell/shell.h
index eb69f669b06d2570968d959ccb82ec6d02d9d3d3..bcb812e269b4e45787a3bc3f39dea2a020d9c2ca 100644
--- a/sky/shell/shell.h
+++ b/sky/shell/shell.h
@@ -10,6 +10,7 @@
 #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;
@@ -33,9 +34,11 @@ class Shell : public SkyView::Delegate {
 
   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);
 };