Do not break in native code (including non-builtin debugger code).

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/300773002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21520 ce2b1a6d-e550-0410-aec6-3dcde31c8c00