Do not force interrupt in test-debug/ProcessDebugMessagesThreaded.

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/557773002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23810 ce2b1a6d-e550-0410-aec6-3dcde31c8c00