For consistency with the PtrComprCageBase struct and the upcoming
PtrComprCage.

Bug: v8:11460
Change-Id: I2e393331c36481ee911edeaf9fb3ff971cfdba83
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2787701
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73874}