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

base/memory/ref_counted.h

Index: base/memory/ref_counted.h
diff --git a/base/memory/ref_counted.h b/base/memory/ref_counted.h
index 439fda44d1ad4505b6c3666af601450ce45d1a43..ad9722e1b991e5265162fac3bb8de5e248d86341 100644
--- a/base/memory/ref_counted.h
+++ b/base/memory/ref_counted.h
@@ -260,9 +260,10 @@ class scoped_refptr {
     // 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;
   }