Fix scoped_refptr copy/move-conversion overload resolution

base/memory/ref_counted.h

 // Copyright (c) 2012 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_MEMORY_REF_COUNTED_H_
 #define BASE_MEMORY_REF_COUNTED_H_
 
 #include <cassert>
 #include <iosfwd>
+#include <type_traits>
 
 #include "base/atomic_ref_count.h"
 #include "base/base_export.h"
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #ifndef NDEBUG
 #include "base/logging.h"
 #endif
 #include "base/threading/thread_collision_warner.h"
 #include "build/build_config.h"
@@ skipping 256 matching lines @@
       AddRef(ptr_);
   }
 
   // Copy constructor.
   scoped_refptr(const scoped_refptr<T>& r) : ptr_(r.ptr_) {
     if (ptr_)
       AddRef(ptr_);
   }
 
   // Copy conversion constructor.
-  template <typename U>
+  template <typename U,
+            typename Dummy = typename std::enable_if<

[danakj, 2016/04/19 23:19:46]

nit: don't need to name it Dummy, just "typename = "

[piman, 2016/04/19 23:24:49]

Done.

+                std::is_convertible<U*, T*>::value>::type>
   scoped_refptr(const scoped_refptr<U>& r) : ptr_(r.get()) {
     if (ptr_)
       AddRef(ptr_);
   }
 
   // Move constructor. This is required in addition to the conversion
   // constructor below in order for clang to warn about pessimizing moves.
   scoped_refptr(scoped_refptr&& r) : ptr_(r.get()) { r.ptr_ = nullptr; }
 
   // Move conversion constructor.
-  template <typename U>
+  template <typename U,
+            typename Dummy = typename std::enable_if<

[danakj, 2016/04/19 23:19:46]

ditto

[piman, 2016/04/19 23:24:49]

Done.

+                std::is_convertible<U*, T*>::value>::type>
   scoped_refptr(scoped_refptr<U>&& r) : ptr_(r.get()) {
     r.ptr_ = nullptr;
   }
 
   ~scoped_refptr() {
     if (ptr_)
       Release(ptr_);
   }
 
   T* get() const { return ptr_; }
@@ skipping 137 matching lines @@
 bool operator!=(const T* lhs, const scoped_refptr<U>& rhs) {
   return !operator==(lhs, rhs);
 }
 
 template <typename T>
 std::ostream& operator<<(std::ostream& out, const scoped_refptr<T>& p) {
   return out << p.get();
 }
 
 #endif  // BASE_MEMORY_REF_COUNTED_H_