Gijs for front-end bits, layout for the new CSS properties and the
removal of nsDeckFrame / nsStackLayout, Jamie and Morgan for the a11y
changes.
As discussed in the bug, the main tricky part here is handling a11y
correctly. For <deck>, that's trivial (just use `visibility: hidden` to
hide the panels visually, while removing the unselected panels from the
a11y tree).
For <tabpanels> however we need to do something special. We do want to
hide stuff visually, but we want to preserve the contents in the a11y
tree.
For that, the easiest fix is introducing a new privileged CSS property
(-moz-subtree-hidden-only-visually), which takes care of not painting
the frame, but marks stuff offscreen in the accessibility tree. This is
not intended to be a property used widely.
Other than that, the changes are relatively straight-forward, though
some of the accessible/mac changes I could get a sanity-check on.
Differential Revision: https://phabricator.services.mozilla.com/D157875
I want to do this so that I can get rid of Either<>. The reasons for getting rid
of either are multiple:
* It doesn't generate as nice C++ code using cbindgen.
* It isn't that nice to use either from Rust.
* cbindgen has bugs with zero-sized types.
I started using this for ColorOrAuto and a few others, for now.
Differential Revision: https://phabricator.services.mozilla.com/D19844
The only reason it was on style_traits is so that they could use it from some
other crates, but Servo eventually ends up getting the value from an integer, so
may as well pass it around and do that in the end of the process anyway.
Differential Revision: https://phabricator.services.mozilla.com/D16557
This is the first step to unprefix user-select.
This has no behavior change, it's just a nicer way to do the same thing which
allows us to unship individual values more easily using parse(condition).
Differential Revision: https://phabricator.services.mozilla.com/D11580
