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

Source/wtf/OwnPtr.h

 /*
  *  Copyright (C) 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  *
  *  This library is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU Library General Public
  *  License as published by the Free Software Foundation; either
  *  version 2 of the License, or (at your option) any later version.
  *
  *  This library is distributed in the hope that it will be useful,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 32 matching lines @@
 #endif
         WTF_DISALLOW_CONSTRUCTION_FROM_ZERO(OwnPtr);
     public:
         typedef typename RemovePointer<T>::Type ValueType;
         typedef ValueType* PtrType;
 
         OwnPtr() : m_ptr(0) { }
         OwnPtr(std::nullptr_t) : m_ptr(0) { }
 
         // See comment in PassOwnPtr.h for why this takes a const reference.
-        template<typename U> OwnPtr(const PassOwnPtr<U>& o);
+        template<typename U> OwnPtr(const PassOwnPtr<U>&, EnsureOwnPtrConvertibleArgDecl(U, T));
 
 #if !COMPILER_SUPPORTS(CXX_RVALUE_REFERENCES)
         // This copy constructor is used implicitly by gcc when it generates
         // transients for assigning a PassOwnPtr<T> object to a stack-allocated
         // OwnPtr<T> object. It should never be called explicitly and gcc
         // should optimize away the constructor when generating code.
         OwnPtr(const OwnPtr<ValueType>&);
 #endif
 
         ~OwnPtr() { deleteOwnedPtr(m_ptr); }
@@ skipping 36 matching lines @@
         // We should never have two OwnPtrs for the same underlying object (otherwise we'll get
         // double-destruction), so these equality operators should never be needed.
         template<typename U> bool operator==(const OwnPtr<U>&) { COMPILE_ASSERT(!sizeof(U*), OwnPtrs_should_never_be_equal); return false; }
         template<typename U> bool operator!=(const OwnPtr<U>&) { COMPILE_ASSERT(!sizeof(U*), OwnPtrs_should_never_be_equal); return false; }
         template<typename U> bool operator==(const PassOwnPtr<U>&) { COMPILE_ASSERT(!sizeof(U*), OwnPtrs_should_never_be_equal); return false; }
         template<typename U> bool operator!=(const PassOwnPtr<U>&) { COMPILE_ASSERT(!sizeof(U*), OwnPtrs_should_never_be_equal); return false; }
 
         PtrType m_ptr;
     };
 
-    template<typename T> template<typename U> inline OwnPtr<T>::OwnPtr(const PassOwnPtr<U>& o)
+    template<typename T> template<typename U> inline OwnPtr<T>::OwnPtr(const PassOwnPtr<U>& o, EnsureOwnPtrConvertibleArgDefn(U, T))
         : m_ptr(o.leakPtr())
     {
     }
 
     template<typename T> inline void OwnPtr<T>::clear()
     {
         PtrType ptr = m_ptr;
         m_ptr = 0;
         deleteOwnedPtr(ptr);
     }
@@ skipping 90 matching lines @@
     template<typename T> inline typename OwnPtr<T>::PtrType getPtr(const OwnPtr<T>& p)
     {
         return p.get();
     }
 
 } // namespace WTF
 
 using WTF::OwnPtr;
 
 #endif // WTF_OwnPtr_h