Bug 20821: Cache property transitions to speed up object initialization

Bug 20821: Cache property transitions to speed up object initialization
https://bugs.webkit.org/show_bug.cgi?id=20821

Reviewed by Cameron Zwarich.

Implement a transition cache to improve the performance of new properties
being added to objects.  This is extremely beneficial in constructors and
shows up as a 34% improvement on access-binary-trees in SunSpider (0.8%
overall)

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@36401 268f45cc-cd09-0410-ab3c-d52691b4dbfc