Type check when upcasting PassOwnPtr/PassOwnArrayPtr to avoid possible function call ambiguousness

Source/wtf/PassOwnArrayPtr.h

 /*
  * Copyright (C) 2010 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 31 matching lines @@
 public:
     typedef T* PtrType;
 
     PassOwnArrayPtr() : m_ptr(0) { }
     PassOwnArrayPtr(std::nullptr_t) : m_ptr(0) { }
 
     // It somewhat breaks the type system to allow transfer of ownership out of
     // a const PassOwnArrayPtr. However, it makes it much easier to work with PassOwnArrayPtr
     // temporaries, and we don't have a need to use real const PassOwnArrayPtrs anyway.
     PassOwnArrayPtr(const PassOwnArrayPtr& o) : m_ptr(o.leakPtr()) { }
-    template<typename U> PassOwnArrayPtr(const PassOwnArrayPtr<U>& o) : m_ptr(o.leakPtr()) { }
+    template<typename U> PassOwnArrayPtr(const PassOwnArrayPtr<U>& o, EnsurePtrConvertibleArgDecl(U, T)) : m_ptr(o.leakPtr()) { }
 
     ~PassOwnArrayPtr() { deleteOwnedArrayPtr(m_ptr); }
 
     PtrType get() const { return m_ptr; }
 
     PtrType leakPtr() const WARN_UNUSED_RETURN;
 
     T& operator*() const { ASSERT(m_ptr); return *m_ptr; }
     PtrType operator->() const { ASSERT(m_ptr); return m_ptr; }
 
@@ skipping 98 matching lines @@
 }
 
 } // namespace WTF
 
 using WTF::PassOwnArrayPtr;
 using WTF::adoptArrayPtr;
 using WTF::const_pointer_cast;
 using WTF::static_pointer_cast;
 
 #endif // WTF_PassOwnArrayPtr_h