to use with Zone. For example, subclasses add constructors that wrap a Zone
in a zone_allocator to save clients this verbosity.

R=bmeurer@chromium.org, mstarzinger@chromium.org
BUG=

Review URL: https://codereview.chromium.org/505133003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23402 ce2b1a6d-e550-0410-aec6-3dcde31c8c00