Get rid of the COUNTERS macro and fetch the counters from a locally
stored isolate instead.

R=karlklose@chromium.org

Review URL: http://codereview.chromium.org/6723014

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7321 ce2b1a6d-e550-0410-aec6-3dcde31c8c00