Check consistency of manual trace and finalization dispatching.

tools/clang/blink_gc_plugin/tests/virtual_and_trace_after_dispatch.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 "virtual_and_trace_after_dispatch.h"
+
+namespace WebCore {
+
+static B* toB(A* a) { return static_cast<B*>(a); }
+
+void A::trace(Visitor* visitor)
+{
+    switch (m_type) {
+    case TB: toB(this)->traceAfterDispatch(visitor);
+    }
+}
+
+void A::traceAfterDispatch(Visitor* visitor)
+{
+}
+
+void B::traceAfterDispatch(Visitor* visitor)
+{
+    visitor->trace(m_a);
+    A::trace(visitor);
+}
+
+}