[ios] WebStateList owns all WebState it manages.

ios/chrome/browser/tabs/tab_model_closing_web_state_observer.h

+// 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_TABS_TAB_MODEL_CLOSING_WEB_STATE_OBSERVER_H_
+#define IOS_CHROME_BROWSER_TABS_TAB_MODEL_CLOSING_WEB_STATE_OBSERVER_H_
+
+#import <Foundation/Foundation.h>
+
+#import "ios/shared/chrome/browser/tabs/web_state_list_observer_bridge.h"
+
+@class TabModel;
+namespace sessions {
+class TabRestoreService;
+}
+
+// Observes WebStateList events about closing WebState.
+@interface TabModelClosingWebStateObserver : NSObject<WebStateListObserving>
+
+- (instancetype)initWithTabModel:(TabModel*)tabModel
+                  restoreService:(sessions::TabRestoreService*)restoreService
+    NS_DESIGNATED_INITIALIZER;
+
+- (instancetype)init NS_UNAVAILABLE;
+
+@end
+
+#endif  // IOS_CHROME_BROWSER_TABS_TAB_MODEL_CLOSING_WEB_STATE_OBSERVER_H_