The three tests that are marked as failures are because they use offsetWidth as a dummy to force a layout flush. Now that these exist, they expose an unrelated bug with reflow.
It's not possible to correctly determine during the css cascade whether the container height
is explicitly specified. Additionally, the spec https://drafts.csswg.org/css2/visudet.html#the-height-property
says this should affect the *used* height, rather than the computed height.
This significantly improves the layout in #6643.
Implement getComputedStyle
It's not quite done but can probably be reviewed anyway.
I still need to finish up a few of the ToCss impls, I just got lazy and wanted to make sure things worked.
The computation of the used values is definitely not right, I'm going to investigate that.
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Passes some but not all WPT tests. One failure is caused by an issue in codegen for the `DOMPointInit` dictionary, the others by outdated tests: Gecko implements an old version of the spec that overloaded the `DOMPoint` constructor to optionally take an object as the first argument, and made `DOMPointReadOnly` non-constructible.
