With this flag enabled, some statistics about the oldspace's freelists
(and free/used spaced in general) are printed before and after each
major garbage collection.

It is useful to get some intuition about fragmentation and debug
freelists. (This flag helped me track down the issues fixed by CLs
1647162 and 1648476)

Additionally, the verbose version (FLAG_trace_gc_freelists_verbose)
prints the freelists of each page of old_space.

Bug: v8:9329
Change-Id: Ifa80426bf9d97ac9950459154507a585b039326d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1655302
Commit-Queue: Darius Mercadier <dmercadier@google.com>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62150}