LGTM.

From battery-status/battery-interface-idlharness.html, however, this is not only an issue of DOMTimeStamp unsupported, but also an issue of typedef unsupported by idlharness.js

[[
typedef unsigned long long DOMTimeStamp;

[TreatNonCallableAsNull]
callback EventHandlerNonNull = any (Event event);
typedef EventHandlerNonNull? EventHandler;
]]