Expose function CheckDebugBreak in the debugger api

API=v8::Debug::CheckDebugBreak
LOG=Y
R=aandrey@chromium.org, vsevik@chromium.org, yurys@chromium.org

Review URL: https://codereview.chromium.org/473913002

Patch from Sergei Vasilinetc <sergeyv@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23227 ce2b1a6d-e550-0410-aec6-3dcde31c8c00