This is not only inherently slow, but it also forces the caller to enter an
Isolate before. Both is bad, so we have to do some heap plumbing.

BUG=v8:2531

Review URL: https://codereview.chromium.org/12217106

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13638 ce2b1a6d-e550-0410-aec6-3dcde31c8c00