Adding overview / layer framework to Activities so that unloaded / sleeping activities can be shown…

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 2621585b3bbf858e1abe0c592dbe6c05e403aaac..7412af224946908dd9839dbb6584bb9f8cf4d1c9 100644
--- a/athena/activity/public/activity_view_model.h
+++ b/athena/activity/public/activity_view_model.h
@@ -54,11 +54,6 @@ class ATHENA_EXPORT ActivityViewModel {
   // implementation.
   virtual views::Widget* CreateWidget() = 0;
 
-  // This gets called before the Activity gets (partially) thrown out of memory
-  // to create a preview image of the activity. Note that even if this function
-  // gets called, |GetOverviewModeImage()| could still return an empty image.
-  virtual void CreateOverviewModeImage() = 0;
-
   // Returns an image which can be used to represent the activity in e.g. the
   // overview mode. The returned image can have no size if either a view exists
   // or the activity has not yet been loaded. In that case