a8a32a972a
MixedViewport didn't use the building:true flag when locking itself, so when it caused a rebuild of its children, we assumed that nobody was allowed to mark things dirty below the list, and things crashed when Inherited people did in fact rebuild. Also: - default offset for MixedViewport - don't bother rebuilding if the underlying RenderObject is going to rebuild anyway for some reason - better docs for the "items must have keys" assert - keep the FlipComponent stuff together in test_widgets.dart