Thus, now there is a "generic" SplayTree and its Zone-bound
specialization ZoneSplayTree.
This is needed for my reimplementation of profiler tree generation in
C++. As generation is performed in a separate thread, Zone can't be
used, because it intentionally not thread-safe.
Review URL: http://codereview.chromium.org/660280
git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3990 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
