Disallow explicit scoped_ptr<T> construction from NULL.

base/memory/scoped_ptr.h

Index: base/memory/scoped_ptr.h
diff --git a/base/memory/scoped_ptr.h b/base/memory/scoped_ptr.h
index dfa12587242962f5884d1f6246aeeca068d16756..c1fed9ae459287323f806195c09fc8ad8fdc9d5e 100644
--- a/base/memory/scoped_ptr.h
+++ b/base/memory/scoped_ptr.h
@@ -432,6 +432,9 @@ class scoped_ptr {
   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