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

ios/shared/chrome/browser/tabs/web_state_list_delegate.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_SHARED_CHROME_BROWSER_TABS_WEB_STATE_LIST_DELEGATE_H_
-#define IOS_SHARED_CHROME_BROWSER_TABS_WEB_STATE_LIST_DELEGATE_H_
-
-#include "base/macros.h"
-
-namespace web {
-class WebState;
-}
-
-// A delegate interface that the WebStateList uses to perform work that it
-// cannot do itself such as attaching tab helpers, ...
-class WebStateListDelegate {
- public:
-  WebStateListDelegate() = default;
-  virtual ~WebStateListDelegate() = default;
-
-  // Notifies the delegate that the specified WebState will be added to the
-  // WebStateList (via insertion/appending/replacing existing) and allows it
-  // to do any preparation that it deems necessary.
-  virtual void WillAddWebState(web::WebState* web_state) = 0;
-
-  // Notifies the delegate that the specified WebState has been detached from
-  // the WebStateList (via detaching/closing/replacing existing) and allows it
-  // to do any clean up that it deems necessary.
-  virtual void WebStateDetached(web::WebState* web_state) = 0;
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(WebStateListDelegate);
-};
-
-#endif  // IOS_SHARED_CHROME_BROWSER_TABS_WEB_STATE_LIST_DELEGATE_H_