Version 3.27.12 (based on bleeding_edge revision r21468)

Check for cached transition to ExternalArray elements kind (issue 3337).

Support ES6 weak collections in heap profiler (Chromium issue 376196).

Performance and stability improvements on all platforms.

git-svn-id: https://v8.googlecode.com/svn/trunk@21472 ce2b1a6d-e550-0410-aec6-3dcde31c8c00