Drive-by-fix:
- fix load spinner z-index

Change-Id: I4a8f9b768ec858da4d91780ae0998a685f4438bf
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2624609Reviewed-by: Sathya Gunasekaran  <gsathya@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72044}