[css-zoom?] zoom: document

[emilio]

WebKit has an exposed zoom: document value which basically "resets" the zoom from ancestors.

This was implemented in WebKit/WebKit@80334b6, but since then Blink must've removed it.

@chrishtr do you know when / why it was removed? I found this useful for scrollbar parts when implementing in Gecko, though I'm not sure there's a more general use case.

cc: #5623 @chrishtr @lilles @smfr @tabatkins @atanassov

[chrishtr]

It was removed in this intent. The rationale is listed there. However, that thread was a bit in the context of considering removing the zoom CSS property at the time.