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

tools/clang/blink_gc_plugin/tests/heap/stubs.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 HEAP_STUBS_H_
 #define HEAP_STUBS_H_
 
 #include "stddef.h"
 
 #define WTF_MAKE_FAST_ALLOCATED                 \
@@ skipping 136 matching lines @@
     virtual void adjustAndMark(Visitor*) const override { }     \
     virtual bool isHeapObjectAlive(Visitor*) const override { return 0; }
 
 #define EAGERLY_FINALIZED() typedef int IsEagerlyFinalizedMarker
 
 template<typename T> class GarbageCollected { };
 
 template<typename T>
 class GarbageCollectedFinalized : public GarbageCollected<T> { };
 
+template<typename T>
+class RefCountedGarbageCollected : public GarbageCollectedFinalized<T> { };
+
 template<typename T> class Member {
 public:
     operator T*() const { return 0; }
     T* operator->() { return 0; }
     bool operator!() const { return false; }
 };
 
 template<typename T> class WeakMember {
 public:
     operator T*() const { return 0; }
@@ skipping 87 matching lines @@
 namespace WTF {
 
 template<typename T>
 struct VectorTraits<blink::Member<T> > {
     static const bool needsDestruction = false;
 };
 
 }
 
 #endif