Allow icomplete types in scoped_refptr<T>.

base/test/opaque_ref_counted.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 BASE_TEST_OPAQUE_REF_COUNTED_H_
 #define BASE_TEST_OPAQUE_REF_COUNTED_H_
 
 #include "base/memory/ref_counted.h"
 
 namespace base {
 
 // OpaqueRefCounted is a test class for scoped_refptr to ensure it still works
 // when the pointed-to type is opaque (i.e., incomplete).
 class OpaqueRefCounted;
 class OpaqueRefCountedThreadSafe;
 
 // Test functions that return and accept scoped_refptr<OpaqueRefCounted> values.
 scoped_refptr<OpaqueRefCounted> MakeOpaqueRefCounted();
 void TestOpaqueRefCounted(scoped_refptr<OpaqueRefCounted> p);
 scoped_refptr<OpaqueRefCountedThreadSafe> MakeOpaqueRefCountedThreadSafe();
 void TestOpaqueRefCountedThreadSafe(
     scoped_refptr<OpaqueRefCountedThreadSafe> p);
 
 }  // namespace base
 
-extern template class scoped_refptr<base::OpaqueRefCounted>;
-extern template class scoped_refptr<base::OpaqueRefCountedThreadSafe>;
-
 #endif  // BASE_TEST_OPAQUE_REF_COUNTED_H_