Tests that client can call undo multiple times with non-empty history.
========= Original ========
<div style="display:none" id="container"> </div>
===== Modified element =====
<div style="display:none" id="container" foo="bar"> </div>
===== Undo 1 =====
<div style="display:none" id="container"> </div>
===== Undo 2 =====
<div style="display:none" id="container"> </div>