Adds the `encryptionScheme` attribute to the `KeySystemTrackConfiguration` dictionary used in `navigator.mediaCapabilities.decodingInfo()`. This allows web applications to query whether a specific encryption scheme (such as `'cenc'` or `'cbcs'`) is supported. *Note: This feature is already approved by the W3C spec and the underlying backend implementation in Chromium already exists. This launch is purely to plumb the `encryptionScheme` property from the Blink IDL layer to the existing backend.*
Currently, Chromium only allows developers to query media capabilities based on codec and `robustness`. With the ecosystem's migration towards the `'cbcs'` encryption scheme, there is significant device fragmentation. Exposing `encryptionScheme` in `decodingInfo()` allows developers to accurately detect if their encrypted media will play. Since the backend support is already implemented, this simply completes the Blink-layer plumbing to match other browsers and the W3C spec.