- storage of enums in bit fields;
 - removing dead entries from address -> id map in HeapObjectsMap;
 - layout of HeapEntry, to avoid class size increase on ia32 due to alignment;

Review URL: http://codereview.chromium.org/3096008

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5217 ce2b1a6d-e550-0410-aec6-3dcde31c8c00