[ios clean] Toolbar displays total number of tabs.

ios/clean/chrome/browser/ui/toolbar/toolbar_mediator.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_CLEAN_CHROME_BROWSER_UI_TOOLBAR_TOOLBAR_MEDIATOR_H_
 #define IOS_CLEAN_CHROME_BROWSER_UI_TOOLBAR_TOOLBAR_MEDIATOR_H_
 
 #import <Foundation/Foundation.h>
 
 #import "ios/shared/chrome/browser/ui/broadcaster/chrome_broadcast_observer.h"
 
 @protocol ToolbarConsumer;
 
 namespace web {
 class WebState;
 }
+class WebStateList;
 
 // A mediator object that provides the relevant properties of a web state
 // to a consumer.
 @interface ToolbarMediator : NSObject<ChromeBroadcastObserver>
 
 // The WebState whose properties this object mediates. This can change during
 // the lifetime of this object and may be null.
 @property(nonatomic, assign) web::WebState* webState;
 
+// The WebStateList that this mediator listens for any changes on the total
+// number of Webstates.
+@property(nonatomic, assign) WebStateList* webStateList;
+
 // The consumer for this object. This can change during the lifetime of this
 // object and may be nil.
 @property(nonatomic, strong) id<ToolbarConsumer> consumer;
 
+// Stops observing all objects.
+- (void)disconnect;
+
 @end
 
 #endif  // IOS_CLEAN_CHROME_BROWSER_UI_TOOLBAR_TOOLBAR_MEDIATOR_H_