Super simple example of adding perf timing to the page display during dev work

perf.js

(function () {
	var perfBar = function(budget) {

		window.onload = function() {
			window.performance = window.performance || window.mozPerformance || window.msPerformance || window.webkitPerformance || {};


			var timing = window.performance.timing,
			now = new Date().getTime(),
			output, loadTime;

			if (!timing) {
				//fail silently
				return;
			}
			budget = budget ? budget : 1000;
			var start = timing.navigationStart;

			var results = document.createElement('div');
			results.setAttribute('id', 'results');
			loadTime = now - start;
			results.innerHTML = (now - start) + "ms";
			if (loadTime > budget) {
				results.className += ' overBudget';
			} else {
				results.className += ' underBudget';
			}
			document.body.appendChild(results);
		}
		
	};
	window.perfBar = perfBar;

}());