12659f2a7b
fixes https://github.com/flutter/flutter/issues/115898
`hasChild` checks `_idToChild` map. `_idToChild` is not assigned until `_callPerformLayout` is called.
So `hasChild` shouldn't be called in `getSize`.
df789c9e76/packages/flutter/lib/src/rendering/custom_layout.dart (L400-L404)
Updated docs and example class names.