Revert of [ios] Move WebStateList to ios/chrome/browser/web_state_list.

ios/chrome/browser/web_state_list/web_state_list_observer.mm

Index: ios/chrome/browser/web_state_list/web_state_list_observer.mm
diff --git a/ios/chrome/browser/web_state_list/web_state_list_observer.mm b/ios/chrome/browser/web_state_list/web_state_list_observer.mm
deleted file mode 100644
index 4567a78926b44ceedde7b3bc7239b6d4e238cad5..0000000000000000000000000000000000000000
--- a/ios/chrome/browser/web_state_list/web_state_list_observer.mm
+++ /dev/null
@@ -1,41 +0,0 @@
-// 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/web_state_list/web_state_list_observer.h"
-
-WebStateListObserver::WebStateListObserver() = default;
-
-WebStateListObserver::~WebStateListObserver() = default;
-
-void WebStateListObserver::WebStateInsertedAt(WebStateList* web_state_list,
-                                              web::WebState* web_state,
-                                              int index) {}
-
-void WebStateListObserver::WebStateMoved(WebStateList* web_state_list,
-                                         web::WebState* web_state,
-                                         int from_index,
-                                         int to_index) {}
-
-void WebStateListObserver::WebStateReplacedAt(WebStateList* web_state_list,
-                                              web::WebState* old_web_state,
-                                              web::WebState* new_web_state,
-                                              int index) {}
-
-void WebStateListObserver::WillDetachWebStateAt(WebStateList* web_state_list,
-                                                web::WebState* web_state,
-                                                int index) {}
-
-void WebStateListObserver::WebStateDetachedAt(WebStateList* web_state_list,
-                                              web::WebState* web_state,
-                                              int index) {}
-
-void WebStateListObserver::WillCloseWebStateAt(WebStateList* web_state_list,
-                                               web::WebState* web_state,
-                                               int index) {}
-
-void WebStateListObserver::WebStateActivatedAt(WebStateList* web_state_list,
-                                               web::WebState* old_web_state,
-                                               web::WebState* new_web_state,
-                                               int active_index,
-                                               bool user_action) {}