Capacity returns allocatable memory and TotalCapacity returns allocatable plus non-allocatable memory for the new space.
BUG=
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/577223002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24040 ce2b1a6d-e550-0410-aec6-3dcde31c8c00