[ios] Add a delegate to WebStateList class.

ios/clean/chrome/browser/model/browser.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_MODEL_BROWSER_H_
 #define IOS_CLEAN_CHROME_BROWSER_MODEL_BROWSER_H_
 
+#include <memory>
+
 #include "base/macros.h"
-#include "ios/shared/chrome/browser/tabs/web_state_list.h"
+
+class WebStateList;
+class WebStateListDelegate;
 
 namespace ios {
 class ChromeBrowserState;
 }
 
 // Browser holds the state backing a collection of Tabs and the attached
 // UI elements (Tab strip, ...).
 class Browser {
  public:
-  explicit Browser(ios::ChromeBrowserState* browser_state);
+  Browser(ios::ChromeBrowserState* browser_state,
+          WebStateListDelegate* web_state_list_delegate);

[rohitrao (ping after 24h), 2017/03/14 11:51:11]

Why is this owned by the BrowserList and passed into the Browser, instead of
just being created and owned by the Browser?

   ~Browser();
 
-  WebStateList& web_state_list() { return web_state_list_; }
-  const WebStateList& web_state_list() const { return web_state_list_; }
+  WebStateList* web_state_list() { return web_state_list_.get(); }
+  const WebStateList* web_state_list() const { return web_state_list_.get(); }
 
   ios::ChromeBrowserState* browser_state() const { return browser_state_; }
 
  private:
-  WebStateList web_state_list_;
   ios::ChromeBrowserState* browser_state_;
+  std::unique_ptr<WebStateList> web_state_list_;
 
   DISALLOW_COPY_AND_ASSIGN(Browser);
 };
 
 #endif  // IOS_CLEAN_CHROME_BROWSER_MODEL_BROWSER_H_