POSIX: Change FD passing test to send many messages
POSIX: Change FD passing test to send many messages

(This is mostly an adoption of Jeremy's patch.)

Also, switch from using /dev/random to /dev/zero. Reading from
/dev/random can drain the system entropy pool and block.

Review URL: http://codereview.chromium.org/21269


git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@9609 0039d316-1c4b-4281-b951-d872f2087c98

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