The approach in this change is to handle the unwrapping/wrapping of the global object transparently with respect to the JS implementation of Object.observe. An alternate approach would be to add a runtime method like %IsJSGlobalProxy and %UnwrapJSGlobalProxy, but it seems ugly to give JS (even implementation JS) access to the unwrapped global.

BUG=v8:2409

Review URL: https://codereview.chromium.org/11414094
Patch from Adam Klein <adamk@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13142 ce2b1a6d-e550-0410-aec6-3dcde31c8c00