[BlinkGCPlugin] Allow tracing member in traceImpl.

tools/clang/blink_gc_plugin/tests/traceimpl.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 TRACEIMPL_H_
+#define TRACEIMPL_H_
+
+#include "heap/stubs.h"
+
+namespace blink {
+
+class X : public GarbageCollected<X> {
+ public:
+  virtual void trace(Visitor*) {}
+};
+
+class TraceImplInlined : public GarbageCollected<TraceImplInlined> {
+ public:
+  void trace(Visitor* visitor) { traceImpl(visitor); }
+
+  template <typename VisitorDispatcher>
+  void traceImpl(VisitorDispatcher visitor) {
+    visitor->trace(m_x);
+  }
+
+ private:
+  Member<X> m_x;
+};
+
+class TraceImplExtern : public GarbageCollected<TraceImplExtern> {
+ public:
+  void trace(Visitor* visitor);
+  template <typename VisitorDispatcher>
+  inline void traceImpl(VisitorDispatcher);
+
+ private:
+  Member<X> m_x;
+};
+}
+
+#endif