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

ios/chrome/browser/web_state_list/web_state_list_metrics_observer.h

Index: ios/chrome/browser/web_state_list/web_state_list_metrics_observer.h
diff --git a/ios/chrome/browser/web_state_list/web_state_list_metrics_observer.h b/ios/chrome/browser/web_state_list/web_state_list_metrics_observer.h
deleted file mode 100644
index e0546f959a4c65d4592332cef422646ef38a4650..0000000000000000000000000000000000000000
--- a/ios/chrome/browser/web_state_list/web_state_list_metrics_observer.h
+++ /dev/null
@@ -1,45 +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.
-
-#ifndef IOS_CHROME_BROWSER_WEB_STATE_LIST_WEB_STATE_LIST_METRICS_OBSERVER_H_
-#define IOS_CHROME_BROWSER_WEB_STATE_LIST_WEB_STATE_LIST_METRICS_OBSERVER_H_
-
-#include "base/macros.h"
-#import "ios/chrome/browser/web_state_list/web_state_list_observer.h"
-
-class WebStateListMetricsObserver : public WebStateListObserver {
- public:
-  WebStateListMetricsObserver();
-  ~WebStateListMetricsObserver() override;
-
-  void ResetSessionMetrics();
-  void RecordSessionMetrics();
-
-  // WebStateListObserver implementation.
-  void WebStateInsertedAt(WebStateList* web_state_list,
-                          web::WebState* web_state,
-                          int 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;
-  void WebStateActivatedAt(WebStateList* web_state_list,
-                           web::WebState* old_web_state,
-                           web::WebState* new_web_state,
-                           int active_index,
-                           bool user_action) override;
-
- private:
-  // Counters for metrics.
-  int inserted_web_state_counter_;
-  int detached_web_state_counter_;
-  int activated_web_state_counter_;
-
-  DISALLOW_COPY_AND_ASSIGN(WebStateListMetricsObserver);
-};
-
-#endif  // IOS_CHROME_BROWSER_WEB_STATE_LIST_WEB_STATE_LIST_METRICS_OBSERVER_H_