[ios] Add a delegate to WebStateList class.

ios/clean/chrome/browser/model/browser_web_state_list_delegate.h

Index: ios/clean/chrome/browser/model/browser_web_state_list_delegate.h
diff --git a/ios/clean/chrome/browser/model/browser_web_state_list_delegate.h b/ios/clean/chrome/browser/model/browser_web_state_list_delegate.h
new file mode 100644
index 0000000000000000000000000000000000000000..b63cb19f87f4e2a71331d2715ce3ef2242f6e181
--- /dev/null
+++ b/ios/clean/chrome/browser/model/browser_web_state_list_delegate.h
@@ -0,0 +1,24 @@
+// 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_MODEL_BROWSER_WEB_STATE_LIST_DELEGATE_H_
+#define IOS_CLEAN_CHROME_BROWSER_MODEL_BROWSER_WEB_STATE_LIST_DELEGATE_H_
+
+#include "base/macros.h"
+#import "ios/shared/chrome/browser/tabs/web_state_list_delegate.h"
+
+// WebStateList delegate for the new architecture.
+class BrowserWebStateListDelegate : public WebStateListDelegate {
+ public:
+  BrowserWebStateListDelegate();
+  ~BrowserWebStateListDelegate() override;
+
+  // WebStateListDelegate implementation.
+  void WillAddWebState(web::WebState* web_state) override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(BrowserWebStateListDelegate);
+};
+
+#endif  // IOS_CLEAN_CHROME_BROWSER_MODEL_BROWSER_WEB_STATE_LIST_DELEGATE_H_