#1260. Another WeakReference tests added

LanguageFeatures/FinalizationRegistry/ffi/WeakReference/weak_reference_target_t09.dart

diff --git a/LanguageFeatures/FinalizationRegistry/ffi/WeakReference/weak_reference_target_t09.dart b/LanguageFeatures/FinalizationRegistry/ffi/WeakReference/weak_reference_target_t09.dart
new file mode 100644
index 0000000..d32b355
--- /dev/null
+++ b/LanguageFeatures/FinalizationRegistry/ffi/WeakReference/weak_reference_target_t09.dart
@@ -0,0 +1,42 @@
+// Copyright (c) 2022, 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.
+
+/// @assertion target property
+/// T? target
+/// The current object weakly referenced by this, if any.
+///
+/// The value is either the object supplied in the constructor, or null if the
+/// weak reference has been cleared.
+///
+/// @description Check that the value of this property value is either the
+/// object supplied in the constructor, or null if the weak reference has been
+/// cleared
+/// @author sgrekhov@unipro.ru
+
+import "dart:async";
+import "../../gc_utils_lib.dart";
+import "../../../../Utils/expect.dart";
+
+class C {
+  int id;
+  C(this.id);
+
+  String toString() => "C($id)";
+}
+
+@pragma('vm:never-inline')
+WeakReference<C> createWeakReference() {
+  C c = C(42);
+  WeakReference<C> wr = WeakReference(c);
+  Future<C>.delayed(Duration(milliseconds: 10), () => c);
+  c = C(-1);
+  return wr;
+}
+
+main() {
+  WeakReference<C> wr = createWeakReference();
+  Expect.isNotNull(wr.target);
+  triggerGc();
+  Expect.isNull(wr.target);
+}