Note: spec has been updated here: http://wiki.ecmascript.org/doku.php?id=harmony:observe_spec_changes.

R=rossberg@chromium.org, rossberg
BUG=v8:2975,v8:2941

Review URL: https://codereview.chromium.org/47703003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17481 ce2b1a6d-e550-0410-aec6-3dcde31c8c00