Returns an integer (0, 1, 2, or 3) representing the index of a given tab.
@param  tab  the ID of the tab element
OR
the tab element itself
function jscoverage_tabIndexOf(tab) {
  if (typeof tab === 'string') {
    tab = document.getElementById(tab);
  }
  var tabs = document.getElementById('tabs');
  var i;
  var child;
  var tabNum = 0;
  for (i = 0; i < tabs.childNodes.length; i++) {
    child = tabs.childNodes.item(i);
    if (child.nodeType === 1) {
      if (child === tab) {
        return tabNum;
      }
      tabNum++;
    }
  }
//#JSCOVERAGE_IF 0
  throw "Tab not found";
//#JSCOVERAGE_ENDIF
}