The benchmarks cover static vs dynamic tracing of an object where the
header is computed statically vs using the object start bitmap,
respectively.

$ out/x64.release/cppgc_basic_benchmarks --benchmark_filter=Trace/*

Running out/x64.release/cppgc_basic_benchmarks
Run on (56 X 3500 MHz CPU s)
CPU Caches:
  L1 Data 32 KiB (x28)
  L1 Instruction 32 KiB (x28)
  L2 Unified 256 KiB (x28)
  L3 Unified 35840 KiB (x2)
Load Average: 0.24, 0.26, 0.26
--------------------------------------------------------
Benchmark              Time             CPU   Iterations
--------------------------------------------------------
Trace/Static        1.78 ns         1.78 ns    393324147
Trace/Dynamic       3.27 ns         3.27 ns    215078276

2020-07-03T15: 21:25+02:00
Change-Id: I8bf5a8ed71a8991873160353e26f96214c038730
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2280099
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68675}