Remove usage of dart:json.

samples/third_party/dromaeo/tests/RunnerSuite.dart

 part of dromaeo;
 
 typedef void Test();
 typedef void Operation();
 typedef void Reporter(Map<String, Result> results);
 
 class Suite {
   /**
    * Ctor.
    *  [:_window:] The window of the suite.
@@ skipping 95 matching lines @@
         'error': result.error,
         'percent': (100.0 * _nRanTests / _nTests)
     });
   }
 
   _postMessage(String command, [var data = null]) {
     final payload = { 'command': command };
     if (data != null) {
       payload['data'] = data;
     }
-    _window.top.postMessage(json.stringify(payload), '*');
+    _window.top.postMessage(JSON.encode(payload), '*');
   }
 
   // Implementation.
 
   final Window _window;
   final String _name;
 
   List<Operation> _operations;
   int _nTests;
   int _nRanTests;
 
   Suite _addOperation(Operation operation) {
     _operations.add(operation);
     return this;
   }
 }