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Leverages mojo EDK utils to remove one platform divergence in pipe creation,
and then another within the Posix world for handling sendmsg vs write which
differs signficantly between SysV-ish Linux and BSDish OsX.

Bug: 
Change-Id: I27391043a05e0c917bed1f99acd3811ef92b2d19
Reviewed-on: https://chromium-review.googlesource.com/578381Reviewed-by: Albert J. Wong <ajwong@chromium.org>
Reviewed-by: Brett Wilson <brettw@chromium.org>
Commit-Queue: Albert J. Wong <ajwong@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488365}