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ea8a57116f
Summary: Previously we computed the list of nodes that need to be notified about layout changes using a list of mutation instructions. That was fine, but that's not really compatible with some other changes that I plan to make, so I decided to change it (make it better). Besides the better design (debatable; fewer dependencies to unrelated moving pieces), here is why I believe the new way is more performant: * The new approach has no `dynamic_casts`, whereas the previous has tons of them (two per a mutation). If a `dynamic_cast` takes 10 ns, for 500 nodes it can take up to 5ms only for casts. (Non-scientific assumption.) * After removing dependency to mutation instruction, we can enable flattening for views which have `onLayout` event. Reviewed By: mdvacca Differential Revision: D15110725 fbshipit-source-id: 31a657ccfd02441734ad1d71a833653223163289