NULL -> nullptr under athena/

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 245902181eb1a5a47cd5ee55665a55365cc2a6b9..69b98f1867719ba7dc36616156508d2c555b31c0 100644
--- a/athena/activity/public/activity_view_model.h
+++ b/athena/activity/public/activity_view_model.h
@@ -45,12 +45,12 @@ class ATHENA_EXPORT ActivityViewModel {
   // draws its own frame.
   virtual bool UsesFrame() const = 0;
 
-  // Returns the contents view which might be NULL if the activity is not
+  // Returns the contents view which might be nullptr if the activity is not
   // loaded. Note that the caller should not hold on to the view since it can
   // be deleted by the resource manager.
   virtual views::View* GetContentsView() = 0;
 
-  // Creates a custom widget for the activity. Returns NULL to use default
+  // Creates a custom widget for the activity. Returns nullptr to use default
   // implementation.
   virtual views::Widget* CreateWidget() = 0;