Fix sky shell.

sky/shell/ui/engine.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_UI_ENGINE_H_
 #define SKY_SHELL_UI_ENGINE_H_
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
@@ skipping 55 matching lines @@
   blink::WebScreenInfo screenInfo() override;
   blink::ServiceProvider* services() override;
 
   // Services methods:
   mojo::NavigatorHost* NavigatorHost() override;
 
   // NavigatorHost methods:
   void RequestNavigate(mojo::Target target,
                        mojo::URLRequestPtr request) override;
   void DidNavigateLocally(const mojo::String& url) override;
+  void RequestNavigateHistory(int32_t delta) override;
 
   void UpdateWebViewSize();
 
   scoped_ptr<PlatformImpl> platform_impl_;
   scoped_ptr<Animator> animator_;
   blink::WebView* web_view_;
   float device_pixel_ratio_;
   gfx::Size physical_size_;
   mojo::Binding<ViewportObserver> viewport_observer_binding_;
 
   base::WeakPtrFactory<Engine> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(Engine);
 };
 
 }  // namespace shell
 }  // namespace sky
 
 #endif  // SKY_SHELL_UI_ENGINE_H_