Make HToFastProperties GC safe.

The runtime call can cause a GC, so the instruction must have proper flags set.

R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/22980003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16173 ce2b1a6d-e550-0410-aec6-3dcde31c8c00