Chrome Version (from "Settings > About Google Chrome"): 2297539ed

Item type is a CollectionViewModel/CollectionViewController concept, used for keeping track of CollectionViewItem.

The CollectionViewItem API mixes currently two concepts: item type and data holder properties.

The goal of the following proposal is to separate both, so that item type stays within the realm of CollectionViewModel/CollectionViewController, while the rest of the API can be used cleanly within the mediator layer.
https://cs.chromium.org/chromium/src/ios/chrome/browser/ui/collection_view/collection_view_model.h