... in order to make it possible to collect zone memory usage stats
from Chrome.

Drive-by-cleanup: move TracingFlags definition to a separate file.

Bug: v8:10572
Change-Id: I05fb65e207d573d5c18821067cfff4c37f2d77cd
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2226561Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68135}