Disallow explicit scoped_ptr<T> construction from NULL.

base/memory/scoped_ptr.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.
 
 // Scopers help you manage ownership of a pointer, helping you easily manage the
 // a pointer within a scope, and automatically destroying the pointer at the
 // end of a scope.  There are two main classes you will use, which correspond
 // to the operators new/delete and new[]/delete[].
 //
 // Example usage (scoped_ptr<T>):
@@ skipping 414 matching lines @@
   template <typename PassAsType>
   scoped_ptr<PassAsType> PassAs() {
     return scoped_ptr<PassAsType>(Pass());
   }
 
  private:
   // Needed to reach into |impl_| in the constructor.
   template <typename U, typename V> friend class scoped_ptr;
   base::internal::scoped_ptr_impl<element_type, deleter_type> impl_;
 
+  // Forbidden for API compatibility with std::unique_ptr.
+  explicit scoped_ptr(int disallow_construction_from_null);
+
   // Forbid comparison of scoped_ptr types.  If U != T, it totally
   // doesn't make sense, and if U == T, it still doesn't make sense
   // because you should never have the same object owned by two different
   // scoped_ptrs.
   template <class U> bool operator==(scoped_ptr<U> const& p2) const;
   template <class U> bool operator!=(scoped_ptr<U> const& p2) const;
 };
 
 template <class T, class D>
 class scoped_ptr<T[], D> {
@@ skipping 252 matching lines @@
 
 // A function to convert T* into scoped_ptr<T>
 // Doing e.g. make_scoped_ptr(new FooBarBaz<type>(arg)) is a shorter notation
 // for scoped_ptr<FooBarBaz<type> >(new FooBarBaz<type>(arg))
 template <typename T>
 scoped_ptr<T> make_scoped_ptr(T* ptr) {
   return scoped_ptr<T>(ptr);
 }
 
 #endif  // BASE_MEMORY_SCOPED_PTR_H_