include what you use: errno.h and string.h in ipc_channel_posix_unittest.cc
include what you use: errno.h and string.h in ipc_channel_posix_unittest.cc

Add missing errno.h include for errno and string.h include for strerror.

Review URL: https://codereview.chromium.org/1409833013

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#358467}

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