N/A. The explainer provides the basic design.
This feature adds support for Curve25519 algorithms in the Web Cryptography API, namely the signature algorithm Ed25519 and the key agreement algorithm X25519.
 RFC 7748, Elliptic Curves for Security
 Daniel Genkin et al, Drive-By Key-Extraction Cache Attacks from Portable Code.
Interoperability and Compatibility
WebCrypto API was specified to allow the addition of new (normalized) crypto algorithms. When an algorithm is not yet supported by a browser, an exception of unrecognized algorithms would be thrown after invoking related APIs.
Firefox: No public signals
Edge: No public signals
Safari: No public signals
Web developers: No signals
Is this feature fully tested by web-platform-tests?
No. The feature is not yet prototyped and the WPTs will be part of the prototype.
Link to entry on the Chrome Platform Status