Temporarily reverting until we figure out how to handle the API cases that use accessors to lazily compute values.
dataAttributeGetterCustom in V8MessageEventCustom (at least) overwrites itself with the computed value using ForceSet. We can either force such clients to first use ForceDelete before caching, use some other caching mechanism; or provide an API for lazily computed properties.

TBR=dcarney@chromium.org
BUG=

Review URL: https://codereview.chromium.org/365903005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22173 ce2b1a6d-e550-0410-aec6-3dcde31c8c00