Previously this is called kWebkitEncryptedMediaEnabled which is mapped to a WebPreference. So the pref string is "webkit.webprefs.encrypted_media_enabled".

Now this is updated to a RendererPreference, with a new pref name kEnableEncryptedMedia. But we are keeping the same pref string "webkit.webprefs.encrypted_media_enabled" to avoid migration issues for now.

At some point, we should do the migration, so that we can move away from the "webkit.webprefs" prefix to avoid the confusion.