src/vs/workbench/common/editor/editorGroupModel.ts/isGroupEditorCloseEvent
export function isGroupEditorCloseEvent(e: IGroupModelChangeEvent): e is IGroupEditorCloseEvent {
	const candidate = e as IGroupEditorCloseEvent;

	return candidate.kind === GroupModelChangeKind.EDITOR_CLOSE && candidate.editorIndex !== undefined && candidate.context !== undefined && candidate.sticky !== undefined;
}