Make sure all destructors are called in HeapHashMap and HeapHashSet

BUG=357113
R=ager@chromium.org, haraken@chromium.org, wibling@chromium.org

Review URL: https://codereview.chromium.org/216723002

git-svn-id: svn://svn.chromium.org/blink/trunk@170443 bbb929c8-8fbe-4397-9dbb-9b2b20218538