A class that parses and stringifies JSON using the browser's built-in JSON
library, if it is avaliable.
Note that the native JSON api has subtle differences across browsers, so
use this implementation with care. See json_test#assertSerialize
for details on the differences from goog.json.
This implementation is signficantly faster than goog.json, at least on
Chrome. See json_perf.html for a perf test showing the difference.