* Revert "Add flow test fixtures and tests (#13986)"
This reverts commit 620f5281b819f304e8e9e945222e26b17b087cc3.
* Revert "Dynamically determine whether to use offscreen surface based on need (#13976)"
This reverts commit a86ef946563b020108320bbfb974bf7343284fd3.
For https://github.com/flutter/flutter/issues/33807
We still need to make layers' children immutable for full immutability.
That will require us to change the SceneBuilder API to build the layer
bottom up instead of top down (post-order traversal instead of pre-order
traversal).