Reland "Refactoring to allow adding new structured types"

Same as before, except that it's now using a void array instead of a struct, to shut up Clang warnings.

R=bmeurer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/224733023

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20574 ce2b1a6d-e550-0410-aec6-3dcde31c8c00