This method is removed since this commit "https://github.com/WebKit/WebKit/commit/7b806050f2bbebb". We should restore this method, in order to be overloaded when we need release the DRM resources. In some proprietary embedded DRM implementation we need to release some resources in order to be able change the DRM system (like passing from PlayReady to Widevine), and start a new playback, without the javascript GC is performed. For example, in some chipsets, we can not initialize the TEE for multiple DRM systems at the same time. In this EME test page "https://ytlr-cert.appspot.com/2020/main.html?test_type=encryptedmedia-test" we change DRM system from Widevine to Playready.
Created attachment 460160 [details] Patch
As I commented on https://bugs.webkit.org/show_bug.cgi?id=223436#c6 . I think you can keep this downstream. It does not belong here anymore.