code: function getElementStyleSheet(element) {
    assertHTMLElement(element);
    return genericPropertyGet(
        Methods.SHEET_GETTER, element, 'sheet', function(sheet) {
          return sheet instanceof CSSStyleSheet;
        });
  }
docs: Returns an element's style without falling prey to things like
  <form><input name="style"></form>.
  @param {!Element} element
  @return {!CSSStyleSheet}