First Paint

firstpaint.js

timing = !!(typeof window.performance !== "undefined" && typeof window.performance.timing !== "undefined");
if (timing && timing.msFirstPaint && window.t_pagestart) {
  t_firstpaint = timing.msFirstPaint - window.t_pagestart;
} else if (window.chrome && typeof window.chrome.loadTimes === 'function') {
  t_firstpaint = window.chrome.loadTimes().firstPaintTime - window.chrome.loadTimes().startLoadTime;
}