Try fixing NaCl V8 compilation failure by initializing interrupt_callback_data_.

TBR=dcarney@chromium.org
BUG=

Review URL: https://codereview.chromium.org/116093006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18376 ce2b1a6d-e550-0410-aec6-3dcde31c8c00