This allows passing commands with quoted spaces, such as:
  tools/test-wrapper-gypbuild.py --special-command \
    "$DR/bin64/drrun -ops '-reset_every_nth_pending 0' @" \
    ...

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/11143018
Patch from Reid Kleckner <rnk@google.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12744 ce2b1a6d-e550-0410-aec6-3dcde31c8c00