Fix invalid ASSERT on 3.27 branch

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/483603005

git-svn-id: https://v8.googlecode.com/svn/branches/3.27@23154 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Version 3.27.34.14 (merged r23084)

Old space cannot be assumed to be iterable between GCs, even if swept precisely.

R=hpayer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/486693002

git-svn-id: https://v8.googlecode.com/svn/branches/3.27@23158 ce2b1a6d-e550-0410-aec6-3dcde31c8c00