Merged r19819 into trunk branch.

Revert "Reland "Enable Object.observe by default""

TBR=machenbach@chromium.org
BUG=v8:2409
LOG=N

Review URL: https://codereview.chromium.org/195503003

git-svn-id: https://v8.googlecode.com/svn/trunk@19820 ce2b1a6d-e550-0410-aec6-3dcde31c8c00