Remove usage of dart:json.

samples/solar3d/web/solar.dart

 // Copyright (c) 2012, 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.
 
 /**
  * A solar system visualization.
  */
 
 library solar3d;
 
 import 'dart:async';
 import 'dart:html';
-import 'dart:json' as json;
+import "dart:convert";
 import 'dart:math' as Math;
 
 import 'package:vector_math/vector_math.dart';
 
 part 'sphere_model_data.dart';
 part 'sphere_model.dart';
 part 'shader.dart';
 part 'planet_shader.dart';
 part 'texture_manager.dart';
 part 'grid.dart';
@@ skipping 502 matching lines @@
     print(log);
   }
 }
 
 /**
  * The entry point to the application.
  */
 void main() {
   application.startup('#container');
 }