Memory infra in tracing currently uses Isolate::GetHeapStatistics to fetch
object statistics from V8 at certain frequency, which is not accurate and will
have redundant result. This path adds a trace event as well as a trace category
at where we collect object statistics after marking before sweeping, and dumps
all information to the trace event.

In order to use this functionality, we need to enable two flags:
--track-gc-object-stats and --noincremental-marking.

BUG=v8:5453

Review-Url: https://codereview.chromium.org/2379823004
Cr-Commit-Position: refs/heads/master@{#39966}