It turns out that an increasing number of persistent handles is a good signal for bugs in the bindings layer

BUG=none
TEST=cctest/test-heap-profiler/PersistentHandleCount

Review URL: https://chromiumcodereview.appspot.com/9620007
Patch from Jochen Eisinger <jochen@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10960 ce2b1a6d-e550-0410-aec6-3dcde31c8c00