TL;DR

• Do not bubble up MeasureInvalidated on scrollable views and pages
• Do not synchronously measure/arrange children on legacy layout upon child measure invalidated: simply wait for the next native layout pass

Description of Change

I executed a speedscope.zip on davidortinau/AllTheLists LearningPage using the latest 8.0.90-ci.net8.24430.1 build.

What I noticed is that #23052 OnChildMeasureInvalidatedInternal was showing up and taking 2% of total time (recursive calls).

This revealed an interesting thing, the time consumed in there is only due to legacy layouts (which includes ContentView) which are triggering synchronous native measurements instead of waiting for the layout pass which is optimized as it runs only once for each invalidated view.

Therefore I realized al that code is actually not needed and substantially wrong.

After these changes, the speedscope looks like this:

As you can see, legacy layout calls and page calls are gone, except for the TemplatedCell of the collection view which is still triggering synchronous measurements.