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A generator is added that outputs some numbers representing our goma
usage. The values have no concrete meaning, but approximate the load
applied to goma for the project and the relative load for different
builders (with some numbers being very rough approximations).

Changes that modify the generated file require a footer in the CL
description in order to submit.

Bug: 1145230
Change-Id: I6d58deee27e9bc6d220f87311a6266c220f03e51
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2556210
Commit-Queue: Garrett Beaty <gbeaty@chromium.org>
Reviewed-by: Erik Staab <estaab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#831871}