Reland "[heap] Attempt to incorporate backing store counters into heap sizing and GC trigger stragery."

This is a reland of ba735dde

Original change's description:
> [heap] Attempt to incorporate backing store counters into heap sizing and GC trigger stragery.
> 
> Bug: chromium:845409
> Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
> Change-Id: Ic62a4339110e3dd2a6b1961a246e2bee0c07c03b
> Reviewed-on: https://chromium-review.googlesource.com/1160162
> Commit-Queue: Rodrigo Bruno <rfbpb@google.com>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#55128}

Bug: chromium:845409
Change-Id: Iaff177f7bebbc073460fab0ae4e5cd9e632e1921
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/1177301Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Rodrigo Bruno <rfbpb@google.com>
Cr-Commit-Position: refs/heads/master@{#55454}