Attempts to allocate memory pages inside the virtual memory cage are
currently allowed to fall back to allocating them outside of the cage if
necessary. When this will be forbidden in the future, these cases will
turn into allocation failures. To estimate the frequency of such events,
we now record the outcome of allocation attempts for memory inside the
cage into UMA.

Bug: chromium:1218005
Change-Id: I788fdd968eea10c887eaba1585cd7951823246e0
Cq-Include-Trybots: luci.v8.try:v8_linux64_heap_sandbox_dbg_ng
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3178520Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Samuel Groß <saelo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77041}