Simplify debug evaluate.

R=peter.rybin@gmail.com
BUG=v8:2585, 173608

Review URL: https://chromiumcodereview.appspot.com/12953002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14019 ce2b1a6d-e550-0410-aec6-3dcde31c8c00