Merged r16265 into 3.20 branch.

Fix migration checks and extend them to the Scavenger.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/23464017

git-svn-id: https://v8.googlecode.com/svn/branches/3.20@16435 ce2b1a6d-e550-0410-aec6-3dcde31c8c00