Use webview in web activity

athena/activity/public/activity_view_model.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 ATHENA_ACTIVITY_PUBLIC_ACTIVITY_VIEW_MODEL_H_
 #define ATHENA_ACTIVITY_PUBLIC_ACTIVITY_VIEW_MODEL_H_
 
 #include <string>
 
 #include "athena/athena_export.h"
 
 typedef unsigned int SkColor;
 
-namespace aura {
-class Window;
+namespace views {
+class View;
 }
 
 namespace athena {
 
 class ATHENA_EXPORT ActivityViewModel {
  public:
   virtual ~ActivityViewModel() {}
 
   // Returns a color most representative of this activity.
   virtual SkColor GetRepresentativeColor() = 0;
 
   // Returns a title for the activity.
   virtual std::string GetTitle() = 0;
 
-  // Returns the native window containing the activity.
-  virtual aura::Window* GetNativeWindow() = 0;
+  // Returns the contents view.
+  virtual views::View* GetContentsView() = 0;
 };
 
 }  // namespace athena
 
 #endif  // ATHENA_ACTIVITY_PUBLIC_ACTIVITY_VIEW_MODEL_H_