src/vs/platform/actions/common/actions.ts/MenuRegistryChangeEvent/for
class MenuRegistryChangeEvent:	static for(id: MenuId): MenuRegistryChangeEvent {
		let value = this._all.get(id);
		if (!value) {
			value = new MenuRegistryChangeEvent(id);
			this._all.set(id, value);
		}
		return value;
	}