Revise the comment on base::IDMap::Replace()

base/id_map.h

Index: base/id_map.h
diff --git a/base/id_map.h b/base/id_map.h
index 8545de84084fc7c116132051754d4222f130c3e8..d171fb14c102cefc5b5ec332315e8a7303f86b9c 100644
--- a/base/id_map.h
+++ b/base/id_map.h
@@ -81,9 +81,8 @@ class IDMap final {
     }
   }
 
-  // Replaces the value for |id| with |new_data| and returns the existing value
-  // (as a unique_ptr<> if in IDMapOwnPointer mode).  Should only be called with
-  // an already added id.
+  // Replaces the value for |id| with |new_data| and returns the existing value.
+  // Should only be called with an already added id.
   V Replace(KeyType id, V new_data) {
     DCHECK(sequence_checker_.CalledOnValidSequence());
     DCHECK(!check_on_null_data_ || new_data);