scoped_refptr: support opaque pointed-to classes via extern template

base/test/opaque_ref_counted.cc

Index: base/test/opaque_ref_counted.cc
diff --git a/base/test/opaque_ref_counted.cc b/base/test/opaque_ref_counted.cc
new file mode 100644
index 0000000000000000000000000000000000000000..ed6c36f1a2decdde05a03b1bf705ea6349dc28b5
--- /dev/null
+++ b/base/test/opaque_ref_counted.cc
@@ -0,0 +1,35 @@
+// 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 "base/test/opaque_ref_counted.h"
+
+#include "base/macros.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace base {
+
+class OpaqueRefCounted : public RefCounted<OpaqueRefCounted> {
+ public:
+  OpaqueRefCounted() {}
+
+  int Return42() { return 42; }
+
+ private:
+  virtual ~OpaqueRefCounted() {}
+
+  friend RefCounted<OpaqueRefCounted>;
+  DISALLOW_COPY_AND_ASSIGN(OpaqueRefCounted);
+};
+
+scoped_refptr<OpaqueRefCounted> MakeOpaqueRefCounted() {
+  return new OpaqueRefCounted();
+}
+
+void TestOpaqueRefCounted(scoped_refptr<OpaqueRefCounted> p) {
+  EXPECT_EQ(42, p->Return42());
+}
+
+}  // namespace base
+
+template class scoped_refptr<base::OpaqueRefCounted>;