[css-properties-values-api] Temporary behavior for <transform-function>.

This CL treats custom properties registered with syntax
<transform-function> as direct CSSStyleValue subclasses, similar to how
e.g. <color> is treated.

This behavior does not get a WPT, because it's not specified (not even as
temporary behavior). It is however consistent with how other "don't know
yet"-types behave in TypedOM, and it's an infinitely more reasonable
temporary behavior that how master currently behaves: a
<transform-function> value becomes CSSUnitValues. For instance,
"transform(10px)" becomes "10px", which is obvious nonsense.

R=futhark@chromium.org

Bug: 641877
Change-Id: Ie06569592192f204d2c05a565458589baeb8378d
Reviewed-on: https://chromium-review.googlesource.com/c/1258328
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Anders Ruud <andruud@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596557}
2 files changed