src/vs/base/common/map.ts/ResourceSet/constructor
class ResourceSet:	constructor(entriesOrKey?: readonly URI[] | ResourceMapKeyFn, toKey?: ResourceMapKeyFn) {
		if (!entriesOrKey || typeof entriesOrKey === 'function') {
			this._map = new ResourceMap(entriesOrKey);
		} else {
			this._map = new ResourceMap(toKey);
			entriesOrKey.forEach(this.add, this);
		}
	}