DCHECK_LE for cr_ngroups vs arraysize(cr_groups)
DCHECK_LE for cr_ngroups vs arraysize(cr_groups)

This DCHECK fails for me locally as

[----------] 3 tests from ProcessInfo
[ RUN      ] ProcessInfo.Self
[70989:10546846:20141216,112509.948519:FATAL process_info_mac.cc:114] Check failed: static_cast<size_t>(ngroups) < (sizeof(ArraySizeHelper(kern_proc_info_.kp_eproc.e_ucred.cr_groups))) (16 vs. 16).
Abort trap: 6

It doesn't seem to happen on the waterfall, so maybe I'm building against
an incorrect header? I don't particularly understand the code, but assuming
it's normal 0-based array, perhaps it should be a DCHECK_LE in any case.

R=mark@chromium.org

Review URL: https://codereview.chromium.org/813473002

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