Port touch-demo.sky to Dart and make it work in SkyShell

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"
 #include "base/single_thread_task_runner.h"
+#include "mojo/public/cpp/bindings/binding.h"
 #include "mojo/public/cpp/system/core.h"
 #include "skia/ext/refptr.h"
 #include "sky/engine/public/web/WebFrameClient.h"
 #include "sky/engine/public/web/WebViewClient.h"
 #include "sky/shell/gpu_delegate.h"
 #include "sky/shell/ui_delegate.h"
 #include "third_party/skia/include/core/SkPicture.h"
 #include "ui/gfx/geometry/size.h"
 
 namespace sky {
 namespace shell {
 class Animator;
 class PlatformImpl;
 
 class Engine : public UIDelegate,
+               public ViewportObserver,
                public blink::WebFrameClient,
                public blink::WebViewClient {
  public:
   struct Config {
     base::WeakPtr<GPUDelegate> gpu_delegate;
     scoped_refptr<base::SingleThreadTaskRunner> gpu_task_runner;
   };
 
   explicit Engine(const Config& config);
   ~Engine() override;
 
   base::WeakPtr<Engine> GetWeakPtr();
 
   void Init(mojo::ScopedMessagePipeHandle service_provider);
 
   void BeginFrame(base::TimeTicks frame_time);
   skia::RefPtr<SkPicture> Paint();
 
  private:
   // UIDelegate methods:
-  void OnViewportMetricsChanged(const gfx::Size& physical_size,
+  void ConnectToViewportObserver(
+      mojo::InterfaceRequest<ViewportObserver> request) override;
+
+  // ViewportObserver:
+  void OnViewportMetricsChanged(int width, int height,
                                 float device_pixel_ratio) override;
+  void OnInputEvent(InputEventPtr event) override;
 
   // WebViewClient methods:
   void initializeLayerTreeView() override;
   void scheduleVisualUpdate() override;
 
   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_