... this reduces the size of VariableMap object by one word which in
turn reduces zone memory pressure. The Scope class which contains
VariableMap as a field is usually in top 5 of all allocated objects
in zone memory.

Bug: v8:9923
Change-Id: I79c6bd9ae97db72f24b831fd5e3733d8d7e4c0fd
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2300486
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68896}