#import [Exposed=(Window)] interface ResizeObserver { constructor(ResizeObserverCallback callback); undefined observe(Element target, optional ResizeObserverOptions options = {}); undefined unobserve(Element target); undefined disconnect(); }; callback ResizeObserverCallback = void (sequence entries, ResizeObserver observer); enum ResizeObserverBoxOptions { "border-box", "content-box", "device-pixel-content-box" }; dictionary ResizeObserverOptions { ResizeObserverBoxOptions box = "content-box"; };