WebStateListObserver methods have default implementation.

ios/chrome/browser/tabs/tab_parenting_observer.mm

 // Copyright 2017 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.
 
 #import "ios/chrome/browser/tabs/tab_parenting_observer.h"
 
 #include "ios/chrome/browser/tab_parenting_global_observer.h"
 #import "ios/chrome/browser/tabs/legacy_tab_helper.h"
 #import "ios/chrome/browser/tabs/tab.h"
 
@@ skipping 12 matching lines @@
 TabParentingObserver::TabParentingObserver() = default;
 
 TabParentingObserver::~TabParentingObserver() = default;
 
 void TabParentingObserver::WebStateInsertedAt(WebStateList* web_state_list,
                                               web::WebState* web_state,
                                               int index) {
   OnWebStateParented(web_state);
 }
 
-void TabParentingObserver::WebStateMoved(WebStateList* web_state_list,
-                                         web::WebState* web_state,
-                                         int from_index,
-                                         int to_index) {}
-
 void TabParentingObserver::WebStateReplacedAt(WebStateList* web_state_list,
                                               web::WebState* old_web_state,
                                               web::WebState* new_web_state,
                                               int index) {
   OnWebStateParented(new_web_state);
 }
-
-void TabParentingObserver::WebStateDetachedAt(WebStateList* web_state_list,
-                                              web::WebState* web_state,
-                                              int index) {}