WebStateListObserver methods have default implementation.

ios/chrome/browser/tabs/tab_parenting_observer.h

Index: ios/chrome/browser/tabs/tab_parenting_observer.h
diff --git a/ios/chrome/browser/tabs/tab_parenting_observer.h b/ios/chrome/browser/tabs/tab_parenting_observer.h
index acb47dc860a5519acd478125552e9fe3bd44dd75..ca75c7889175d43971c74b9277e1cac5904d7eed 100644
--- a/ios/chrome/browser/tabs/tab_parenting_observer.h
+++ b/ios/chrome/browser/tabs/tab_parenting_observer.h
@@ -17,17 +17,10 @@ class TabParentingObserver : public WebStateListObserver {
   void WebStateInsertedAt(WebStateList* web_state_list,
                           web::WebState* web_state,
                           int index) override;
-  void WebStateMoved(WebStateList* web_state_list,
-                     web::WebState* web_state,
-                     int from_index,
-                     int to_index) override;
   void WebStateReplacedAt(WebStateList* web_state_list,
                           web::WebState* old_web_state,
                           web::WebState* new_web_state,
                           int index) override;
-  void WebStateDetachedAt(WebStateList* web_state_list,
-                          web::WebState* web_state,
-                          int index) override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(TabParentingObserver);