Merge verbatim descriptors from other (the descriptor of the map being updated) rather than this (descriptors of the most updated map found in the transition tree).

BUG=v8:2863
R=svenpanne@chromium.org

Review URL: https://chromiumcodereview.appspot.com/23676003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16396 ce2b1a6d-e550-0410-aec6-3dcde31c8c00