function getUpgradedListOfElement_(element) {
	    var dataUpgraded = element.getAttribute('data-upgraded');
	    // Use `['']` as default value to conform the `,name,name...` style.
	    return dataUpgraded === null ? [''] : dataUpgraded.split(',');
	  }
Class constructor for icon toggle MDL component.
Implements MDL component design pattern defined at:
https://github.com/jasonmayes/mdl-component-design-pattern

@constructor
@param {HTMLElement} element The element that will be upgraded.