Currently, the RenderFrameObserver::DidMeaningfulLayout hook is an introspection API for Chrome services (like Distiller, Translate, phishing, etc.). It runs after a layout had happened -- so that the tree is clean and you could, for example, run a TextIterator without forcing another layout.

The timing of this callback, while technically correct, is not necessarily right for RAIL. For example, we should not run any Chrome service code in the middle of a critical rendering path.

Instead, we need to consider moving this API to be something that runs at the idle time. Now that we have a scheduler to tell us when that is.