Only install JitCodeEventHandler for GDB JIT if requested.

TBR=dslomov@chromium.org

Review URL: https://codereview.chromium.org/381883005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22330 ce2b1a6d-e550-0410-aec6-3dcde31c8c00