src/vs/platform/undoRedo/common/undoRedoService.ts/UndoRedoService/hasElements
class UndoRedoService:	public hasElements(resource: URI): boolean {
		const strResource = this.getUriComparisonKey(resource);
		if (this._editStacks.has(strResource)) {
			const editStack = this._editStacks.get(strResource)!;
			return (editStack.hasPastElements() || editStack.hasFutureElements());
		}
		return false;
	}