Fix invalid attributes when generalizing because of incompatible map change.

BUG=382143
LOG=y
TEST=mjsunit/regress/regress-382143
R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/324933003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21743 ce2b1a6d-e550-0410-aec6-3dcde31c8c00