[BUGFIX release] Avoid unnecessary change events during initial render #11935
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This change reduces unnecessary event firing during the initial render of each component. In my sample scenario, it cut average events per component from 14.9 to 7.07.
(The seven remaining events are the ones that are supposed to fire once each: didInitAttrs, didInsertElement, didReceiveAttrs, didRender, init, willInsertElement, and willRender.)
The impact on actual render time is not necessarily large (a few scenarios I looked at improved by up to 10%), but applications that are doing more expensive work in their observers may see bigger benefits.
This change is based on @stefanpenner's investigation in this comment. It's built on top of @rwjblue's PR #11934, since it would otherwise conflict and is attacking a related problem.
My changes are relatively small, you can see them in isolation here.