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Including GPU, GPU.FYI and Dawn testers for trunk and M85.
Also includes some small changes for consistency:
- Don't specify GOMA backend for testers
- Don't specify cores dimension on Mac (some are 4 and some 8 core)

This is 2nd CL out of 3 moving these GCEs into luci.chromium.gpu.ci pool.

1. crrev.com/i/3295888
  Allocate GCEs in luci.chromium.gpu.ci pool and increase chrome-gpu quota
2. This CL:
  Switch GPU CI testers to trigger tasks in luci.chromium.gpu.ci pool
3. crrev.com/i/3295890
  Remove GCEs from luci.chomium.ci pool and decrease chrome-desktop quota

Bug: 1132439
Change-Id: I385b625271b510816e322b0aa93e317634c59c88
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2434087Reviewed-by: Garrett Beaty <gbeaty@chromium.org>
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811799}