Version 3.20.1

Implemented WeakMap.prototype.clear function. (issue 2753)

Ensure CheckInitialized is present independent of define. (Chromium issue 255779)

Performance and stability improvements on all platforms.

git-svn-id: https://v8.googlecode.com/svn/trunk@15448 ce2b1a6d-e550-0410-aec6-3dcde31c8c00