Check that classes with non-trivial destructors have finalization support.

tools/clang/blink_gc_plugin/tests/class_requires_finalization_mixin.cpp

+// Copyright 2014 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.
+
+#include "class_requires_finalization_mixin.h"
+
+namespace WebCore {
+
+void Mixin::trace(Visitor* visitor)
+{
+    visitor->trace(m_onHeap);
+}
+
+void NeedsFinalizer::trace(Visitor* visitor)
+{
+    visitor->trace(m_obj);
+    Mixin::trace(visitor);
+}
+
+void HasFinalizer::trace(Visitor* visitor)
+{
+    visitor->trace(m_obj);
+    Mixin::trace(visitor);
+}
+
+}