Move FileDescriptorShuffle to base/posix. This file is very posix-specific.

TEST=it compiles
BUG=none

Review URL: https://codereview.chromium.org/10399100

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@166970 0039d316-1c4b-4281-b951-d872f2087c98
6 files changed