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Specifically, this replaces exit code 106 (COULD_NOT_CREATE_PROCESS)
with six new codes to help diagnose these failures.

BUG=672813

Change-Id: I6a482761c34ae06c4f438aa2a30d7bd69afdf819
Reviewed-on: https://chromium-review.googlesource.com/601987Reviewed-by: Sigurður Ásgeirsson <siggi@chromium.org>
Commit-Queue: Greg Thompson <grt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#492009}