Summary: This is purely for the performance improvement; Achieving predictable O(1) fast flat tree traversal.
Since there can be a still tricky case in wild where our web tests couldn't catch, I would like to enable it on trunk now so that we can know how things are going well on Canary.
See the explainer for the actual performance improvements.
I'll update the explainer once YouTube finishes migration from Web Components v0
to Web Components v1. I expect YouTube is one of the customers who get performance improvements.
In terms of impacts on Blink developers:
Nothing. The usage of FlatTreeTraversal doesn't change.
Please file a bug if you see any bug which can be related to a flat tree structure.
Since a flat tree is now being used almost everywhere in Blink, this launch can have positive impacts on the performance of style calc, layout tree construction, event dispatching, hit tests, and almost everything in our rendering pipeline.
I hope there is no regression. If a regression happens and a fix is non-trivial, I'll disable the flag.
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Hayato