Add support for PerformanceObserver, performance.measure() and performance.mark()

[RaisinTen]

It might be worth implementing the PerformanceObserver API as well as the performance.measure() and performance.mark() APIs on the performance object in

jsdom/lib/jsdom/living/hr-time/Performance-impl.js

Lines 1 to 22 in 2f8a730

	"use strict";
	const EventTargetImpl = require("../events/EventTarget-impl").implementation;
	class PerformanceImpl extends EventTargetImpl {
	constructor(globalObject, args, privateData) {
	super(globalObject, args, privateData);
	this.timeOrigin = privateData.timeOrigin;
	this._nowAtTimeOrigin = privateData.nowAtTimeOrigin;
	}
	now() {
	return performance.now() - this._nowAtTimeOrigin;
	}
	toJSON() {
	return { timeOrigin: this.timeOrigin };
	}
	}
	exports.implementation = PerformanceImpl;