Reload the descriptor after modifying the transition target.

R=danno@chromium.org
BUG=chromium:282736

Review URL: https://chromiumcodereview.appspot.com/23658033

git-svn-id: https://v8.googlecode.com/svn/branches/3.20@16619 ce2b1a6d-e550-0410-aec6-3dcde31c8c00