Helper to print first paint time in Chrome

firstpaint.js

(function() {
  'use strict';

  // First paint perf.
  if (window.chrome && window.chrome.loadTimes) {
    const getFP = function() {
      let load = chrome.loadTimes();
      let fp = (load.firstPaintTime - load.startLoadTime) * 1000;
      return Math.round(fp);
    };

    window.onload = e => {
      let render = () => {
        let fp = getFP();
        console.log(`${fp} ms`);
        document.title += ' - ' + fp + ' ms fp';
      };
      window.setTimeout(render, 100); // Wait a tick so we're guaranteed a fp time.
    };
  }
})();