Limited recursion in regexp compilation by a budget. (Chromium issue 178790)

ES6 symbols: Implemented Symbol intrinsic and basic functionality (issue 2158)

Performance and stability improvements on all platforms.

git-svn-id: http://v8.googlecode.com/svn/trunk@13808 ce2b1a6d-e550-0410-aec6-3dcde31c8c00