Move isolate tests to lib/isolate.

tests/language/deferred_in_isolate_app.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.
-
-import 'deferred_in_isolate_lib.dart' deferred as test;
-
-void main(args, msg) {
-  assert(args != null);
-  assert(args.length == 1);
-  assert(msg != null);
-  assert(msg.length == 1);
-
-  var expectedMsg = args[0];
-  var replyPort = msg[0];
-
-  try {
-    print("BeforeLibraryLoading");
-
-    test.loadLibrary().then((_) {
-      var obj = new test.DeferredObj(expectedMsg);
-      replyPort.send(obj.toString());
-    }).catchError((error) {
-      replyPort.send("Error from isolate:\n$error");
-    });
-  } catch (exception, stacktrace) {
-    replyPort.send("Exception from isolate:\n$exception\n$stacktrace");
-  }
-}