Correctly handle instances without elements in polymorphic keyed load/store (Chromium issue 331416).

Fix selection of popular pages in store buffer (Chromium issue 331444).

Prepare removal of ObjectTemplate::New without Isolate parameter (Chromium issue 324225).

Performance and stability improvements on all platforms.

git-svn-id: http://v8.googlecode.com/svn/trunk@18488 ce2b1a6d-e550-0410-aec6-3dcde31c8c00