Not TAG-reviewed yet at this very early stage.
Introduce new @font-face descriptors to override the default font metrics (ascent, descent, etc.)
1. Improve interoperably across browsers and operating systems, so that the same font always looks the same on the same site, regardless of OS or browser. See 
2. Align metrics between two web fonts present simultaneously, but for different glyphs. This use case example comes from the crostini terminal 
3. Override font metrics for a fallback font to emulate a web font, in order to minimize Cumulative Layout Shift.
Interoperability and Compatibility
This new feature is still at a very early stage. We will follow the standards process and hopefully reach a resolution at CSSWG, so that the interop risks are minimized.
Gecko: No signal
WebKit: No signal
Web developers: No signals
Will this feature be supported on all six Blink platforms (Windows, Mac, Linux,
Chrome OS, Android, and Android WebView)?
Is this feature fully tested by web-platform-tests?
Will be added when the spec stabilizes.
Link to entry on the Chrome Platform Status