Prevent crashpad from uploading on Mac from tests and bots.
Prevent crashpad from uploading on Mac from tests and bots.

Background: 59.47% of all Mac crashes from version 45.0.2452.0 show
"--test-type=browser" on the command line, have symbols unknown
to the crash server, and have URLs like:
  http://127.0.0.1:52769/banners/manifest_no_type_test_page.html#sw_activated
corresponding to particular browsertest cases.

The noise generated by these reports greatly hinders our efforts to
assess the stability of what we're shipping to users, and can obscure
real problems elsewhere.

As a solution, this patch attempts to force-off, rather than force-on,
crash uploading while running headless (as on bots). The force-on
behavior is the root cause of these crash uploads, and it was a
mistranslation of breakpad's logic to force-on crash reporting
(not uploading) from bots.

BUG=467908

Review URL: https://codereview.chromium.org/1232433002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#338740}

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