GC plugin: RefPtr<T> is legal if T is RefCountedGC-derived.

tools/clang/blink_gc_plugin/tests/ref_ptr_to_gc_managed_class.h

 // 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.
 
 #ifndef REF_PTR_TO_GC_MANAGED_CLASS_H_
 #define REF_PTR_TO_GC_MANAGED_CLASS_H_
 
 #include "heap/stubs.h"
 
 namespace blink {
 
 class HeapObject;
 
 class PartObject {
     DISALLOW_ALLOCATION();
 private:
     RefPtr<HeapObject> m_obj;
 };
 
 class HeapObject : public GarbageCollectedFinalized<HeapObject> {
 public:
     void trace(Visitor*);
 private:
     PartObject m_part;
     Vector<RefPtr<HeapObject> > m_objs;
 };
 
+class RefHeapObject : public RefCountedGarbageCollected<HeapObject> {
+public:
+    void trace(Visitor*);
+private:
+    PartObject m_part;
+    Vector<RefPtr<RefHeapObject> > m_objs;
+};
+
 }
 
 #endif