Fill in one-word-fillers for the unused property fields.

BUG=chromium:240056

Review URL: https://chromiumcodereview.appspot.com/15247003
Patch from Toon Verwaest <verwaest@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14714 ce2b1a6d-e550-0410-aec6-3dcde31c8c00