Avoid calling `builder` in `ConstrainedLayoutBuilder` when layout constraints are the same.
[Design doc](flutter.dev/go/layout-builder-optimization).
## Related Issues
Fixes https://github.com/flutter/flutter/issues/6469
* [Slider] Rebase.
* disabled thumb color with alphaBlend of colorScheme surface
* test remove alphablend
* Change rectangular track to how it used to be
* Chaned to adaptive slider
* blank lines
Co-authored-by: Will Larche <larche@google.com>
Move Flutter Gallery to dev/integration_tests/ as it is an older copy used only for testing. The current version of the Flutter Gallery now lives in https://github.com/flutter/gallery.
