Add opener-opened relationship between WebState in WebStateList.

ios/chrome/browser/tabs/tab_model.h

 // Copyright 2012 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_H_
 #define IOS_CHROME_BROWSER_TABS_TAB_MODEL_H_
 
 #import <Foundation/Foundation.h>
 #import <UIKit/UIKit.h>
 
@@ skipping 224 matching lines @@
 
 // Closes ALL the tabs.
 - (void)closeAllTabs;
 
 // Halts all tabs (terminating active requests) without closing them. Used
 // when the app is shutting down.
 - (void)haltAllTabs;
 
 // Notifies observers that the given |tab| was changed.
 - (void)notifyTabChanged:(Tab*)tab;
+
 // Notifies observers that the snapshot for the given |tab| changed was changed
 // to |image|.
 - (void)notifyTabSnapshotChanged:(Tab*)tab withImage:(UIImage*)image;
 
 // Adds |observer| to the list of observers. |observer| is not retained. Does
 // nothing if |observer| is already in the list. Any added observers must be
 // explicitly removed before the TabModel is destroyed.
 - (void)addObserver:(id<TabModelObserver>)observer;
 
 // Removes |observer| from the list of observers.
@@ skipping 48 matching lines @@
 // TYPED.
 - (Tab*)insertTabWithURL:(const GURL&)URL
                 referrer:(const web::Referrer&)referrer
               windowName:(NSString*)windowName
                   opener:(Tab*)parentTab
                  atIndex:(NSUInteger)index;
 
 @end
 
 #endif  // IOS_CHROME_BROWSER_TABS_TAB_MODEL_H_