Refactor trap invocation.
Test other Object.prototype functionality for proxies.

R=ager@chromium.org
BUG=v8:1543
TEST=

Review URL: http://codereview.chromium.org/7436004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8707 ce2b1a6d-e550-0410-aec6-3dcde31c8c00