Bug 1007862 - Update name of barriered base class in  SpiderMonkey's GDB pretty-printers, r=jimb,sfink

This patch fixes test failures in js/src/gdb/tests/test-Root.py.

js::PreBarriered is no longer the common base class for SpiderMonkey's GC graph
edge types; now js::BarrieredBase is the best choice for pretty-printers to
support. Also, there is no longer a separate hierarchy for non-pointer types
(eg JS::Value). Update the pretty-printers and their tests.

--HG--
extra : rebase_source : 9c8190c47fcdb5be60c94e20b2eebdfff2394c96