Spill and merge virtual frames explicitly in the deferred code.

Account for the fact that the inlined write barrier size depends on
the size of the new space masks.

Review URL: http://codereview.chromium.org/3018015

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5122 ce2b1a6d-e550-0410-aec6-3dcde31c8c00