Add support for the CSS `revert` keyword/value
Add support for the CSS `revert` keyword/value

This patch adds autocomplete support for the CSS `revert` keyword.
`revert` is a valid value for any property.

p { all: revert; } resets to the default <p> browser styles.

Chromium CL temporarily disabling affected tests:
https://chromium-review.googlesource.com/c/chromium/src/+/2169647
Chromium CL restoring affected tests:
https://chromium-review.googlesource.com/c/chromium/src/+/2169908

Tweet: https://twitter.com/mathias/status/1251107357804900352
Bug: chromium:579788, chromium:1075437
Change-Id: I098bf2af9355f9f041b22311dc1c735993ae04f5
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2168093
Reviewed-by: Alex Rudenko <d8d88e7d7e77f69e23d1d1432231196fb8e02a62@chromium.org>
Commit-Queue: Mathias Bynens <17a2cbc4e33156874a9862b0f530521117e66a3d@chromium.org>
Auto-Submit: Mathias Bynens <17a2cbc4e33156874a9862b0f530521117e66a3d@chromium.org>

ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend