Fix DebugEvaluate on properties defined on Object.prototype

BUG=415499
R=yangguo
LOG=N

Review URL: https://codereview.chromium.org/592033002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24119 ce2b1a6d-e550-0410-aec6-3dcde31c8c00