Create json package.

pkg/json/lib/json.dart

Index: pkg/json/lib/json.dart
diff --git a/sdk/lib/json/json.dart b/pkg/json/lib/json.dart
similarity index 99%
copy from sdk/lib/json/json.dart
copy to pkg/json/lib/json.dart
index 5fd3a6ae20c0da9e60d0738eaa4e5959abbe91d7..58b6c796d6135abbc02ed18dda51d1c6ed7a2e98 100644
--- a/sdk/lib/json/json.dart
+++ b/pkg/json/lib/json.dart
@@ -6,7 +6,7 @@
  * Utilities for encoding and decoding JSON (JavaScript Object Notation) data.
  */
 
-library dart.json;
+library json;
 
 // JSON parsing and serialization.
 
@@ -66,9 +66,7 @@ class JsonCyclicError extends JsonUnsupportedObjectError {
  *
  * Throws [FormatException] if the input is not valid JSON text.
  */
-external parse(String json, [reviver(var key, var value)]);
-
-_parse(String json, reviver(var key, var value)) {
+parse(String json, [reviver(var key, var value)]) {
   BuildJsonListener listener;
   if (reviver == null) {
     listener = new BuildJsonListener();