The current version uses SetObjectProperty which will not set the
value in case this is a readonly property. The spec explictly says
that a configurable but non writable property can have its value
changed with Object.defineProperty (because the same thing can be
accomplished by doing 3 calls (set writable to true, update the value,
set writable to false).
Review URL: http://codereview.chromium.org/6518004
git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6766 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
