GitLab

Set up a feature flag and corresponding state inside cc to enable
using HUD for displaying performance metrics. Currently when we enable
the show performance metrics flag we only add WebVitals metrics, which
comes from Blink. We might want to add other metrics in the future.

R=sadrul

Bug: 1149385
Change-Id: I437e113a5fc4f44c6fbaa542c92d1f2da6cbb393
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2540570
Commit-Queue: weiliangc <weiliangc@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828221}