This changes the GC histograms from HistogramTimer to TimedHistogram.

Bug: chromium:898613
Change-Id: Ie18c6dd3b958c3ce93f0f84faec0f306d699afa0
Reviewed-on: https://chromium-review.googlesource.com/c/1299241
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57036}