Toolbar not supporting IE11 (realXHR.responseURL)

[Martin-4Spaces]

This fine piece of code

// Track all AJAX requests
var oldXHR = window.XMLHttpRequest;

function newXHR() {
	var realXHR = new oldXHR();
	realXHR.addEventListener("readystatechange", function() {
		// Only success responses and URLs that do not contains "debugbar_time" are tracked
		if (realXHR.readyState === 4 && realXHR.status.toString()[0] === '2' && **realXHR.responseURL.indexOf**('debugbar_time') === -1) {
			var debugbarTime = realXHR.getResponseHeader('Debugbar-Time');
			if (debugbarTime) {
				var h2 = document.querySelector('#ci-history > h2');
				h2.innerHTML = 'History <small>You have new debug data.</small> <button onclick="loadDoc(' + debugbarTime + ')">Update</button>';
				var badge = document.querySelector('a[data-tab="ci-history"] > span > .badge');
				badge.className += ' active';
			}
		}
	}, false);
	return realXHR;
}

window.XMLHttpRequest = newXHR;

Located here assumes responseURL exists on realXHR. This is not true for IE11. https://stackoverflow.com/questions/8056277/how-to-get-response-url-in-xmlhttprequest
Instead it results in an error "Unable to get property 'indexOf' of undefined or null reference".