Original report by me.

Support for persistent licenses (VMP) requires CDM host verification and CDM storage ID (related GN config). Persistent license requirements can be seen in the CanSupportPersistentLicense function. CDM host verification requires the existence of sig files (example) and the implementation of AddContentDecryptionModules.

Not all CEF clients will provide sig files (which require a signing certificate from Google). Chromium (here) will selectively enable CDM host verification at runtime if valid sig files exist.