sky/shell should link with sky/engine

sky/engine/public/platform/ServiceProvider.h

 // Copyright 2014 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_ENGINE_PUBLIC_PLATFORM_SERVICEPROVIDER_H_
 #define SKY_ENGINE_PUBLIC_PLATFORM_SERVICEPROVIDER_H_
 
 namespace mojo {
 class NavigatorHost;
-class Shell;
 }
 
 namespace blink {
 
 class ServiceProvider {
  public:
   virtual mojo::NavigatorHost* NavigatorHost() = 0;
-  virtual mojo::Shell* Shell() = 0;
 
  protected:
   virtual ~ServiceProvider();
 };
 
 } // namespace blink
 
 #endif  // SKY_ENGINE_PUBLIC_PLATFORM_SERVICEPROVIDER_H_