Use Widget frame and WidgetDelegate in ActvityWidget

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 "athena/common/athena_export.h"
 #include "base/strings/string16.h"
 
 typedef unsigned int SkColor;
 
 namespace views {
 class View;
 }
 
 namespace athena {
 
 class ATHENA_EXPORT ActivityViewModel {
  public:
   virtual ~ActivityViewModel() {}
 
   // Called after the view model is attaced to the widget/window tree.
   virtual void Init() = 0;
 
   // Returns a color most representative of this activity.
-  virtual SkColor GetRepresentativeColor() = 0;
+  virtual SkColor GetRepresentativeColor() const = 0;
 
   // Returns a title for the activity.
-  virtual base::string16 GetTitle() = 0;
+  virtual base::string16 GetTitle() const = 0;
+
+  // True if the activity wants to use Widget's frame, or false if the activity
+  // draws its own frame.
+  virtual bool UsesFrame() const = 0;
 
   // Returns the contents view.
   virtual views::View* GetContentsView() = 0;
 };
 
 }  // namespace athena
 
 #endif  // ATHENA_ACTIVITY_PUBLIC_ACTIVITY_VIEW_MODEL_H_