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.

TBR=sadrul, bokan@chromium.org

Bug: 1149385
Change-Id: I718ef95d782ee2f1bb3ac13dd296e48b0c3e25bb
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-Original-Commit-Position: refs/heads/master@{#828221}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2545088Reviewed-by: weiliangc <weiliangc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828579}