Add webgl_conformance telemetry tests to the CrOS amd64-generic VM CQ bot.

Adds it at 100% experimental. Will move it out of experimental if
everything's stable.

There should be available capacity for this in pool:Chrome-CrOS-VM. Reasoning is:

- telemetry_perf_unittests consumes about 20 bot_hours per hour during peak (see
https://console.cloud.google.com/bigquery?sq=575346572923:851e224a05214590bd41c0486ea71b5a)

- webgl_conformance test runtime is 2.9 times that of telemetry_perf_unittests:
50:33 (http://shortn/_CMLRnWNnU2 ) vs 17:23 min (http://shortn/_19BVdlzsz5)

- assuming similar trigger & flake rate of the two suites, expected bot_hours per hour
during peak for webgl_conformance is 2.9 times that of telemetry_perf_unittests

- webgl_conformance should need 2.9 x 20 = 60 bots

- the pool currently has almost exactly 60 bots unused during peak load: http://shortn/_2DGaCAXhof

- so we should have capacity!

Bug: 957807
Change-Id: I7f0212bae0bb8a2e156cbef286f670fdf72798d9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1588168
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663226}
6 files changed