Rename and fix json frog library in SDK

frog/lib/json.js

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-// JavaScript implementation of the native methods declared in json.dart.
-
-// TODO(jmesserly): this needs lots of cleanup.
-// Ideally JS objects could be treated as Dart Maps directly, and then we can
-// really use native JSON.parse and JSON.stringify.
-
-
-var $JSON = JSON; // Save the real JSON
-
-JSON = function() {};
-JSON.parse = function(str) {
-  return $JSON.parse(str, function(k, v) { return $convertJsToDart(v); });
-}
-
-// Shallow-converts the parsed JavaScript value into a Dart object, and
-// returns the Dart object.
-// Any component values have already been converted.
-function $convertJsToDart(obj) {
-  if (obj != null && typeof obj == 'object' && !(obj instanceof Array)) {
-    return $fixupJsObjectToDartMap(obj);
-  }
-  return obj;
-}
-
-// Converts the parsed JavaScript Object into a Dart Map.
-function $fixupJsObjectToDartMap(obj) {
-  var map = new HashMapImplementation();
-  var keys = Object.keys(obj);
-  for (var i = 0; i < keys.length; i++) {
-    map.$setindex(keys[i], obj[keys[i]]);
-  }
-  return map;
-}
-
-///////////////////////////////////////////////////////////////////////////////
-
-JSON.stringify = function(obj) {
-  return $JSON.stringify(obj, $convertDartToJs);
-}
-
-// TODO(jmesserly): better error message!
-function UnconvertibleException() {}
-
-// Converts the Dart object into a JavaScript value, suitable for applying
-// JSON.stringify to.
-// Throws UnconvertibleException if the Dart value is not convertible.
-function $convertDartToJs(key, obj) {
-  // Only Dart Maps need to be converted into JavaScript objects.
-  if (obj === null || obj === undefined) {
-    return null;
-  }
-  switch (typeof obj) {
-    case 'boolean':
-    case 'number':
-    case 'string':
-      return obj;
-    case 'object':
-      if (obj instanceof Array) {
-        return obj;
-      } else {
-        try {
-          return $convertDartMapToJsObject(obj);
-        } catch (e) {
-          // TODO(jmesserly): HACK: assume a failure means it's not a Map, and
-          // throw UnconvertibleException below...
-        }
-      }
-  }
-  $throw(new UnconvertibleException());
-}
-
-// Converts the Dart Map into a JavaScript object.
-// Converts only shallowly.
-function $convertDartMapToJsObject(map) {
-  var obj = {};
-  var propertyNames = map.getKeys();
-  for (var i = 0, len = propertyNames.length; i < len; i++) {
-    var propertyName = propertyNames[i];
-    obj[propertyName] = map.$index(propertyName);
-  }
-  return obj;
-}