This fixes failures on bots running with --extra-flags=--future

Change-Id: I9594f44db9cc749d02151b695300b5c888f2c99b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2617085
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71973}