Revert "lazy instantiation of the default isolate" and "build fix for 17049".

This reverts r17049 and r17060.

TBR=dcarney@chromium.org

Review URL: https://codereview.chromium.org/25697002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17066 ce2b1a6d-e550-0410-aec6-3dcde31c8c00