Instead of doing a restyle whenever layout is requested, only do one if
script believes that the `Document` has changed in a way that needs a
restyle. In addition, track the different reasons this might be the
case. This will be used later to provide better debugging output.
In layout, when a restyle isn't requested, provide:
- an early return if layout is up-to-date enough for the reflow goal.
- skipping restyle and reflow if it isn't necessary.
Testing: This should not change observable behavior, and thus is covered
by existing tests.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>
3e1cdacd07