Fix scoped_refptr assignment operator in the case of having it as a member.

base/memory/ref_counted.h

 // Copyright (c) 2011 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_
 #pragma once
 
 #include "base/atomic_ref_count.h"
 #include "base/base_export.h"
@@ skipping 242 matching lines @@
   T* release() {
     T* retVal = ptr_;
     ptr_ = NULL;
     return retVal;
   }
 
   scoped_refptr<T>& operator=(T* p) {
     // AddRef first so that self assignment should work
     if (p)
       p->AddRef();
-    if (ptr_ )
-      ptr_ ->Release();
+    T* old_ptr = ptr_;
     ptr_ = p;
+    if (old_ptr)
+      old_ptr->Release();
     return *this;
   }
 
   scoped_refptr<T>& operator=(const scoped_refptr<T>& r) {
     return *this = r.ptr_;
   }
 
   template <typename U>
   scoped_refptr<T>& operator=(const scoped_refptr<U>& r) {
     return *this = r.get();
@@ skipping 14 matching lines @@
 };
 
 // Handy utility for creating a scoped_refptr<T> out of a T* explicitly without
 // having to retype all the template arguments
 template <typename T>
 scoped_refptr<T> make_scoped_refptr(T* t) {
   return scoped_refptr<T>(t);
 }
 
 #endif  // BASE_MEMORY_REF_COUNTED_H_