crbug 83877)

The issue was that with the relatively small start and increment size of the string we created a ton of string handles when scanning a large string with special characters (500k+ in this case).

In addition, since we can not be sure the the newly allocated string
is in newspace a check is introduced and if not a filler object is
inserted instead of shrinking.
Review URL: http://codereview.chromium.org/7075009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8082 ce2b1a6d-e550-0410-aec6-3dcde31c8c00