dpwas: Setup Origin Trial for Window Controls Overlay

Setup origin trial and a feature counter

Explainer: https://github.com/WICG/window-controls-overlay/blob/master/explainer.md
Design Doc: https://docs.google.com/document/d/1k0YL_-VMLIfjYCgJ2v6cMvuUv2qMKg4BgLI2tJ4qtyo/edit?usp=sharing
I2P: https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/cper6nNLFRQ/hU91kfCWBQAJ

Bug: 937121
Change-Id: I1090b46d6694c42da7260037813cbea2329f651d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2843564
Commit-Queue: Hassan Talat <hatalat@microsoft.com>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Alan Cutter <alancutter@chromium.org>
Reviewed-by: Chase Phillips <cmp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#881046}