Revert "[Object.observe] Don't force normalization of elements for observed objects"

Broke ARM build

TBR=danno
BUG=

Review URL: https://codereview.chromium.org/66603004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17602 ce2b1a6d-e550-0410-aec6-3dcde31c8c00