[ios] Add a delegate to WebStateList class.

ios/chrome/browser/tabs/tab_model_web_state_list_delegate.h

Index: ios/chrome/browser/tabs/tab_model_web_state_list_delegate.h
diff --git a/ios/chrome/browser/tabs/tab_model_web_state_list_delegate.h b/ios/chrome/browser/tabs/tab_model_web_state_list_delegate.h
new file mode 100644
index 0000000000000000000000000000000000000000..d783b7e9b888182852b864a9cd95b4410e5a1db9
--- /dev/null
+++ b/ios/chrome/browser/tabs/tab_model_web_state_list_delegate.h
@@ -0,0 +1,29 @@
+// 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_WEB_STATE_LIST_DELEGATE_H_
+#define IOS_CHROME_BROWSER_TABS_TAB_MODEL_WEB_STATE_LIST_DELEGATE_H_
+
+#import "base/ios/weak_nsobject.h"
+#include "base/macros.h"
+#import "ios/shared/chrome/browser/tabs/web_state_list_delegate.h"
+
+@class TabModel;
+
+// WebStateList delegate for the old architecture.
+class TabModelWebStateListDelegate : public WebStateListDelegate {
+ public:
+  explicit TabModelWebStateListDelegate(TabModel* tab_model);
+  ~TabModelWebStateListDelegate() override;
+
+  // WebStateListDelegate implementation.
+  void WillAddWebState(web::WebState* web_state) override;
+
+ private:
+  base::WeakNSObject<TabModel> tab_model_;
+
+  DISALLOW_COPY_AND_ASSIGN(TabModelWebStateListDelegate);
+};
+
+#endif  // IOS_CHROME_BROWSER_TABS_TAB_MODEL_WEB_STATE_LIST_DELEGATE_H_