`class type performanceObserverInit = object ... end`
`class type performanceEntry = object ... end`
`class type performanceObserverEntryList = object ... end`
`class type performanceObserver = object ... end`
`val performanceObserver : ((performanceObserverEntryList Js.t -> performanceObserver Js.t -> unit) Js.callback -> performanceObserver Js.t) Js.constr`
`val is_supported : unit -> bool`
`val observe : entry_types:string list -> f:(performanceObserverEntryList Js.t -> performanceObserver Js.t -> unit) -> performanceObserver Js.t`