Previously, WR would attempt to detect at the start of frame
building if the spatial node of any picture cache contained
a non-axis-aligned transform, and disable picture caching in
that edge case.
However, picture caching can't (currently) be disabled when the
native compositor is active. In this mode, picture caching was
force enabled, causing an assertion failure due to unexpected
coordinate systems when updating pictures.
This patch changes the way the detection of scroll root logic
works such that we don't consider any scroll frame inside a
reference frame to be a valid scroll root for picture caching
purposes. Thus it's not possible to create a picture cache
where the reference spatial node has a non-axis-aligned transform.
Differential Revision: https://phabricator.services.mozilla.com/D75890
af3ddc2628