Skip octane/pdfjs for now in debug mode because slow.

TBR=rossberg@chromium.org
TEST=benchmarks/octane/pdfjs

Review URL: https://codereview.chromium.org/569243002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23950 ce2b1a6d-e550-0410-aec6-3dcde31c8c00