Bug 1800358 - Fix invalid scroll root selection in some cases. r=gfx-reviewers,jrmuizel

Reverts an optimization that can cause artifacts on some pages. We
need to do a deeper investigation at some point to find out why,
and then reenable the optimization.

Differential Revision: https://phabricator.services.mozilla.com/D168026

gfx/wr/webrender/src/tile_cache.rs

@@ -243,12 +243,7 @@ impl TileCacheBuilder {
             .collect();
 
         scroll_root_occurrences.retain(|parent_spatial_node_index, _| {
-            let parent_is_root = spatial_tree.is_root_coord_system(*parent_spatial_node_index);
-
             scroll_roots.iter().all(|child_spatial_node_index| {
-                let child_is_root = spatial_tree.is_root_coord_system(*child_spatial_node_index);
-
-                (parent_is_root && child_is_root) ||
                 parent_spatial_node_index == child_spatial_node_index ||
                 spatial_tree.is_ancestor(
                     *parent_spatial_node_index,