Disentangle field from transition stores.

Review URL: https://chromiumcodereview.appspot.com/14063006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14223 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fix JSON.stringify's slow path wrt sliced strings.

R=mvstanton@chromium.org
BUG=229923

Review URL: https://chromiumcodereview.appspot.com/14107004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14224 ce2b1a6d-e550-0410-aec6-3dcde31c8c00