Bug 838398 - Make sure SyncType.onDestroy() is called when AboutHomePromoBox is removed. r=mfinkle

--HG--
rename : services/sync/tests/unit/test_utils_json.js => services/common/tests/unit/test_utils_json.js
extra : rebase_source : 4e9db7d7954d9138776bcfc1812764dcfa7bc989