Since we're not reserving memory anymore, we don't log reserved memory
when profiling serialization. So, instead log the allocation counts used
by OutputStatistics as a pseudo-reserved size.

Bug: v8:10998
Bug: chromium:1075999
Change-Id: I64dc6086b14c0e720ef8d0c1ea99a6f8ccabcf9c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2460808
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70399}