With this fix, we only create the enum cache for own property descriptors (originally we cached all descriptors in the map).  The problem was that the size of all descriptors could be trimmed during GC triggered by allocating the storage for the cache, so we could have ended up with a wrong storage size.

This is really Toon's fix, I have only created a small repro case.

BUG=
R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/212673011

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20308 ce2b1a6d-e550-0410-aec6-3dcde31c8c00