The CL makes sure to extract and copy Oilpan young GC metrics to
v8::metrics::GarbageCollectionYoungCycle. In addition, it makes sure
that metrics are not reported twice by bailing out from
GCTracer::NotifyCppGCCompleted() for young GC cycles (the metrics are
reported later in Heap::CollectGarbage() by calling
GCTracer::StopCycle()).

Bug: chromium:1029379
Change-Id: I07bf51e85a76a7cdbeeb8d87c9072edf2634158b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3545168Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79766}