HGraphBuilder::BuildJSObjectCheck: Tighten instance type comparison

R=danno@chromium.org

Review URL: https://codereview.chromium.org/366083005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22206 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Hydrogen LoopBuilder: add support for "while(true) {...}" loops

R=danno@chromium.org

Review URL: https://codereview.chromium.org/368243002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22207 ce2b1a6d-e550-0410-aec6-3dcde31c8c00