Fail more gracefully with bad zygote command line flags

If --no-zygote is given, --no-sandbox must be used too. Previously this
caused a check failure and a crash dump upload, but with this patch we
instead log an error and exit with a failure status.

BUG=721323

Change-Id: I88cd8f1cbd11bdaf8476bea663bf679badd92712
Reviewed-on: https://chromium-review.googlesource.com/509529
Reviewed-by: Charlie Reis <creis@chromium.org>
Commit-Queue: Sami Kyöstilä <skyostil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#473257}
1 file changed