Initial JS stub implementation of Object.observe. Adds support for .object/.unobserve/.notify/.deliverChangeRecords. No delivery mechanism is implemented for end-of-microtask.

Review URL: https://codereview.chromium.org/11225058
Patch from Rafael Weinstein <rafaelw@google.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12819 ce2b1a6d-e550-0410-aec6-3dcde31c8c00