Version 3.26.17 (based on bleeding_edge revision r20788)

Clear invalid field maps in PropertyAccessInfo (Chromium issue 363956).

ES6: Add support for Map/Set forEach (Chromium issues 1793, 2323).

Performance and stability improvements on all platforms.

git-svn-id: https://v8.googlecode.com/svn/trunk@20789 ce2b1a6d-e550-0410-aec6-3dcde31c8c00