Dart: Reorganize files

mojo/dart/unittests/embedder_tests/validation_test.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:isolate';
 import 'dart:mojo.builtin' as builtin;
 import 'dart:typed_data';
 
@@ skipping 116 matching lines @@
     try {
       await runTest(name, parser.parse(data), expected);
       print('$name PASSED.');
     } catch (e) {
       print('$name FAILED: $e');
     }
   }
   // TODO(zra): Add integration tests when they no longer rely on Client=
   MojoHandle.reportLeakedHandles();
 }