[heap] Announce whether GC was forced in tracing scopes

This information is used on the metrics side to filter out forced GCs at
the beginning of benchmark runs.

Bug: 843903
Change-Id: Ia57ee25fb51afbcf06d541a30e3d1f6b51e95557
Reviewed-on: https://chromium-review.googlesource.com/c/1268937
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597861}
1 file changed