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According to crbug.com/412186, there is some incorrect handle management in
NaClProcessHost. It's much easier to use base::File to manage closing the
socket handles, and it cleans up some weirdness with directly using NaClHandle
as well.

BUG=412186

Review URL: https://codereview.chromium.org/552183004

Cr-Commit-Position: refs/heads/master@{#294511}