Double allocation size for special json strings on every resize (fixes

Double allocation size for special json strings on every resize (fixes
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