Version 3.26.20 (based on bleeding_edge revision r20866)

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@20867 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Merge remote-tracking branch 'upstream/trunk' into trunk