Linux: make --renderer-startup-dialog work on Linux.
Linux: make --renderer-startup-dialog work on Linux.

This is needed, along with --enable-sandbox-debugging, to debug SUID
sandboxed renderers.

With this patch, one can run:
  ./out/Debug/chrome --enable-sandbox-debugging --renderer-startup-dialog

Then, in GDB, attach to the PID which is printed to stderr and
continue. Then send SIGUSR1 to the PID to resume the renderer.

http://codereview.chromium.org/159211


git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@21303 0039d316-1c4b-4281-b951-d872f2087c98

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