fix: null check on elapsedTime for some browsers (#7213)

src/tracing/utils.ts

@@ -2,7 +2,8 @@
  * Returns the time elapsed between page load and now.
  * @param markName the identifier for the performance mark to be created and measured.
  */
-export function calculateElapsedTimeWithPerformanceMark(markName: string): number {
+export function calculateElapsedTimeWithPerformanceMark(markName: string): number | undefined {
   const elapsedTime = performance.mark(markName)
+  if (!elapsedTime) return undefined
   return elapsedTime.startTime
 }