Function maybePumpEarlyFrame

src/runtime.js:510–522

* If it makes sense, let the browser paint the current frame before * executing the callback. * @param {!Window} win * @param {function()} cb Callback that should run after a frame was * pumped.

(win, cb)

 *     pumped.
 */
function maybePumpEarlyFrame(win, cb) {
  // There is definitely nothing to draw yet, so we might as well
  // proceed.
  if (!win.document.body) {
    cb();
    return;
  }
  if (hasRenderDelayingServices(win)) {
    cb();
    return;
  }
  Services.timerFor(win).delay(cb, 1);
}