Move isolate tests to lib/isolate.

tests/language/deferred_in_isolate_test.dart

-// Copyright (c) 2014, 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.
-
-// Test that deferred libraries are supported from isolates other than the root
-// isolate.
-
-import 'dart:isolate';
-
-main() {
-  try {
-    var receivePort = new RawReceivePort();
-    var expectedMsg = "Deferred Loaded.";
-
-    receivePort.handler = (msg) {
-      if (msg != expectedMsg) {
-        print("Test failed.");
-        throw msg;  // Fail the test if the message is not expected.
-      }
-      print('Test done.');
-      receivePort.close();
-    };
-
-    var stopwatch = new Stopwatch()..start();
-    Isolate.spawnUri(new Uri(path: 'deferred_in_isolate_app.dart'),
-                             [expectedMsg],
-                             [receivePort.sendPort]).then((isolate) {
-      print('Isolate spawn: ${stopwatch.elapsedMilliseconds}ms');
-    }).catchError((error) {
-      print(error);
-    });
-  } catch (exception, stackTrace) {
-    print('Test failed.');
-    print(exception);
-    print(stackTrace);
-    rethrow;
-  }
-}