Expose allocated and used byte counters for the different spaces. The goal is
to monitor those values both on page cycles and via UMA

BUG=v8:2201
TEST=none

Review URL: https://chromiumcodereview.appspot.com/10657022
Patch from Jochen Eisinger <jochen@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11931 ce2b1a6d-e550-0410-aec6-3dcde31c8c00