Version 3.28.8 (based on bleeding_edge revision r22114)

Remove static initializer from isolate.

ES6: Add missing Set.prototype.keys function (issue 3411).

Introduce debug events for promises (issue 3093).

Performance and stability improvements on all platforms.

git-svn-id: https://v8.googlecode.com/svn/trunk@22115 ce2b1a6d-e550-0410-aec6-3dcde31c8c00