Not having a copy-assignment operator is a massive footgun (as it won't call the
right constructors / destructors). :(
Filed https://bugzilla.mozilla.org/show_bug.cgi?id=1604075 for an analysis that
would've caught this.
One of my WIP patches adding a heap allocation to LengthPercentage caught this.
While at it, add non-const versions of the arrow and deref operators and fix
operator!= too (which doesn't compile, but we don't use it so C++'s template
madness says it's just fine).
Differential Revision: https://phabricator.services.mozilla.com/D57257
--HG--
extra : moz-landing-system : lando
5da9cf54f6