src/vs/workbench/common/notifications.ts/NotificationHandle/registerListeners
class NotificationHandle:	private registerListeners(): void {

		// Visibility
		this._register(this.item.onDidChangeVisibility(visible => this._onDidChangeVisibility.fire(visible)));

		// Closing
		Event.once(this.item.onDidClose)(() => {
			this._onDidClose.fire();

			this.dispose();
		});
	}