Revert "Various cleanup/simplification in object-observe.js"

It broke the context snapshot by trying to get ahold of the
per-isolate observation_state object too early.

This reverts commit a137cb74fb8f89fabcb0396bebb0bdf248c4b0ae.

TBR=yangguo@chromium.org

Review URL: https://codereview.chromium.org/692473002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24977 ce2b1a6d-e550-0410-aec6-3dcde31c8c00