This requires adding a new JSObject to the strong root list and populating it from
object-observe.js. The main other change is that we now directly use ObjectHashTable
from JS rather than using WeakMap, since using the latter would end up leaking whichever
Context initialized that observation state.

Added a test via the API showing that different contexts all end up working on the same state.

Review URL: https://codereview.chromium.org/11274014
Patch from Adam Klein <adamk@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12873 ce2b1a6d-e550-0410-aec6-3dcde31c8c00