Revert r14023 (Unify code for fast and slow path of JSON.stringify) from trunk.

R=jkummerow@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/12993003

git-svn-id: https://v8.googlecode.com/svn/trunk@14039 ce2b1a6d-e550-0410-aec6-3dcde31c8c00