There were two kinds of layout tracing controlled by the same debugging
option:
- modern layout: Functionality that dumped a JSON serialization of the
layout tree before and after layout.
- legacy layout: A scope based tracing that reported the process of
layout in a structured way.
I don't think anyone working on layout is using either of these two
features. For modern layout requiring data structure to implement
`serde` serialization is incredibly inconvenient and also generates a
lot of extra code.
We also have a more modern tracing functionality based on perfetto that
we have started to use for layout and IMO it's actually being used and
more robust.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
