A change to a counter "definition" propagates to all subsequent
instances of this counter: descendents, siblings and their descendents
(the "next tree slice"). Rebuilding the layout tree (from the parent
node) covers at least the "next_tree_slice".
When position changes, we may need to make larger structural updates
to the layout tree. A simple relayout is not sufficient.
This was a source of flakiness in the engine, and gives us at least
+28 new WPT subtest passes.
Because we cache the transformed text string in text nodes affected by
text-transform, we have to actually update the layout tree when this
property value changes.
