Fix MUST_USE_RESULT warning.

R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/228203003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20561 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Revert "Refactoring to allow adding new structured types"

This reverts commit r20538 for breaking gcmole.

TBR=rossberg@chromium.org

BUG=

Review URL: https://codereview.chromium.org/228223002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20562 ce2b1a6d-e550-0410-aec6-3dcde31c8c00