Allocate a new empty number dictionary when resetting elements

BUG=410332
LOG=y
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/545773003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23727 ce2b1a6d-e550-0410-aec6-3dcde31c8c00