Function startPhaseTimer

code/redux/public/app.js:7963–7975

(fiber, phase)

}

function startPhaseTimer(fiber, phase) {
  if (enableUserTimingAPI) {
    if (!supportsUserTiming) {
      return;
    }
    clearPendingPhaseMeasurement();
    if (!beginFiberMark(fiber, phase)) {
      return;
    }
    currentPhaseFiber = fiber;
    currentPhase = phase;
  }
}

function stopPhaseTimer() {
  if (enableUserTimingAPI) {