[ios] Add a delegate to WebStateList class.

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

Index: ios/clean/chrome/browser/model/browser_list.h
diff --git a/ios/clean/chrome/browser/model/browser_list.h b/ios/clean/chrome/browser/model/browser_list.h
index 184718c46db058b13a99ccf91a3379ba02126138..8219507496e1a01c2d2285d54d436c7397e04205 100644
--- a/ios/clean/chrome/browser/model/browser_list.h
+++ b/ios/clean/chrome/browser/model/browser_list.h
@@ -5,12 +5,15 @@
 #ifndef IOS_CLEAN_CHROME_BROWSER_MODEL_BROWSER_LIST_H_
 #define IOS_CLEAN_CHROME_BROWSER_MODEL_BROWSER_LIST_H_
 
+#include <memory>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/supports_user_data.h"
 #include "ios/clean/chrome/browser/model/browser.h"
 
+class WebStateListDelegate;
+
 namespace ios {
 class ChromeBrowserState;
 }
@@ -39,8 +42,9 @@ class BrowserList : public base::SupportsUserData::Data {
   void CloseBrowserAtIndex(int index);
 
  private:
-  std::vector<std::unique_ptr<Browser>> browsers_;
   ios::ChromeBrowserState* browser_state_;
+  std::unique_ptr<WebStateListDelegate> delegate_;
+  std::vector<std::unique_ptr<Browser>> browsers_;
 
   DISALLOW_COPY_AND_ASSIGN(BrowserList);
 };