Add display refresh rate to about://gpu on Chrome OS

Some gpu bugs are related to the monitor refresh rate. Adding this display
information will help us on gpu debugging.

Bug: 964095
Change-Id: I54d468dd192110a77f2aa46f7d441ed257f06491
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1644232
Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Commit-Queue: Maggie Chen <magchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#666313}