athena: Introduce ActivityView.

athena/activity/public/activity_view_model.h

Index: athena/activity/public/activity_view_model.h
diff --git a/athena/activity/public/activity_view_model.h b/athena/activity/public/activity_view_model.h
index c22c863144229b6f825aa0ccb99d8595d03b1b6e..b6f9a5646817e10f279459a05d3385d00ea0dac3 100644
--- a/athena/activity/public/activity_view_model.h
+++ b/athena/activity/public/activity_view_model.h
@@ -21,6 +21,8 @@ class Widget;
 
 namespace athena {
 
+class ActivityView;
+
 // The view model for the representation of the activity.
 class ATHENA_EXPORT ActivityViewModel {
  public:
@@ -41,6 +43,10 @@ class ATHENA_EXPORT ActivityViewModel {
   // Returns an icon for the activity.
   virtual gfx::ImageSkia GetIcon() const = 0;
 
+  // Sets the ActivityView for the model to update. The model does not take
+  // ownership of the view.
+  virtual void SetActivityView(ActivityView* view) = 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;