Remove usage of dart:json.

sdk/lib/_internal/dartdoc/lib/src/json_serializer.dart

Index: sdk/lib/_internal/dartdoc/lib/src/json_serializer.dart
diff --git a/sdk/lib/_internal/dartdoc/lib/src/json_serializer.dart b/sdk/lib/_internal/dartdoc/lib/src/json_serializer.dart
index 9f9915ab08d1f54af03df6fcb8e9fadb5427774b..8bfa7bb6ca4ac7cea4178969a2f09bfbcaf50af5 100755
--- a/sdk/lib/_internal/dartdoc/lib/src/json_serializer.dart
+++ b/sdk/lib/_internal/dartdoc/lib/src/json_serializer.dart
@@ -10,8 +10,8 @@
 library json_serializer;
 
 import 'dart:async';
+import 'dart:convert';
 import 'dart:mirrors';
-import 'dart:json' as json;
 
 String serialize(Object o) {
   var printer = new JsonPrinter();
@@ -207,7 +207,7 @@ class JsonPrinter {
     } else {
       // Convenient hack to remove the pretty printing this serializer adds by
       // default.
-      return json.stringify(json.parse(_sb.toString()));
+      return JSON.encode(JSON.decode(_sb.toString()));
     }
   }