a mark-sweep.  We have a soft limit on old space size, which is designed to
trigger an old-space collection when we hit it.  Unfortunately although the
soft limit had already triggered an old space collection, the soft limit was
preventing objects from new space from being promoted.  For every promotion
candidate we were checking 3 different ways to allocate in old space before
giving up and putting the object in the other semispace.  This change allows
the promoted objects to go to old space and also makes us more eager to
sweep a page before trying other ways to find space for an object.
Review URL: http://codereview.chromium.org/8748005

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10092 ce2b1a6d-e550-0410-aec6-3dcde31c8c00