[css-paint-api] Computed vs. specified values in inputArguments

[andruud]

What is the rationale behind passing specified values to the worklet via inputArguments? E.g. if I do paint(foo, 1em), I'm currently supposed to get (if we ignore that it can't be reified, #895) a CSSUnitValue with 1em. Isn't it more useful to have that em actually resolve against the font-size before passing it to the worklet?

cc @bfgeek

[tabatkins]

Yeah, custom functions (including these specialized ones we're providing) should be treated as computed values, and thus their argument should be computed as much as possible.