posix: ignore SIGPIPE in all processes, not just the browser
posix: ignore SIGPIPE in all processes, not just the browser

E.g. plugin<->renderer channel can go down, causing SIGPIPE instead of a
normal error.

Review URL: http://codereview.chromium.org/155390

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@20448 0039d316-1c4b-4281-b951-d872f2087c98

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