[ios] Use web_state_list in web_contents_mediator.

ios/clean/chrome/browser/ui/web_contents/web_coordinator.h

 // Copyright 2016 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_WEB_CONTENTS_WEB_COORDINATOR_H_
 #define IOS_CLEAN_CHROME_BROWSER_UI_WEB_CONTENTS_WEB_COORDINATOR_H_
 
 #import "ios/shared/chrome/browser/ui/coordinators/browser_coordinator.h"
 
-namespace web {
-class WebState;
-}
-
 // A coordinator for a UI element that displays the web view associated with
-// |webState|.
+// the current active web state.
 @interface WebCoordinator : BrowserCoordinator
-
-// The web state this coordinator is displaying.
-@property(nonatomic, assign) web::WebState* webState;
-
 @end
 
 #endif  // IOS_CLEAN_CHROME_BROWSER_UI_WEB_CONTENTS_WEB_COORDINATOR_H_