run = function() {
				var readyState = document.readyState || "";

				timerId = setTimeout(run, readyState === "loading" ? 200 :  999);
				if ( document.body ) {
					pf.fillImgs();
					isDomReady = isDomReady || regReady.test(readyState);
					if ( isDomReady ) {
						clearTimeout( timerId );
					}

				}
			}
Takes a candidate object with a srcset property in the form of url/
ex. "images/pic-medium.png 1x, images/pic-medium-2x.png 2x" or
    "images/pic-medium.png 400w, images/pic-medium-2x.png 800w" or
    "images/pic-small.png"
Get an array of image candidates in the form of
     {url: "/foo/bar.png", resolution: 1}
where resolution is http://dev.w3.org/csswg/css-values-3/#resolution-value
If sizes is specified, res is calculated