This replaces the fixed expansion policy based on number of scavenges.
Increased the max new space size to 8MB (only reserved space).
Increased the defalt new space size to 512KB.

Review URL: http://codereview.chromium.org/125046

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2151 ce2b1a6d-e550-0410-aec6-3dcde31c8c00