[ios] Change API to inform WebStateList of opener-opened relationship.

ios/clean/chrome/browser/ui/tab_grid/tab_grid_coordinator.mm

 // Copyright 2016 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.
 
 // ======                        New Architecture                         =====
 // =         This code is only used in the new iOS Chrome architecture.       =
 // ============================================================================
 
 #import "ios/clean/chrome/browser/ui/tab_grid/tab_grid_coordinator.h"
 
@@ skipping 35 matching lines @@
 
 #pragma mark - Properties
 
 - (void)setBrowser:(Browser*)browser {
   [super setBrowser:browser];
 
   for (int i = 0; i < 7; i++) {
     web::WebState::CreateParams webStateCreateParams(browser->browser_state());
     std::unique_ptr<web::WebState> webState =
         web::WebState::Create(webStateCreateParams);
-    self.webStateList.InsertWebState(0, webState.release(), nullptr);
+    self.webStateList.InsertWebState(0, webState.release());
   }
   self.webStateList.ActivateWebStateAt(0);
 }
 
 - (WebStateList&)webStateList {
   return self.browser->web_state_list();
 }
 
 #pragma mark - BrowserCoordinator
 
@@ skipping 36 matching lines @@
   std::unique_ptr<web::WebState> closedWebState(
       self.webStateList.DetachWebStateAt(index));
 }
 
 - (void)createAndShowNewTab {
   web::WebState::CreateParams webStateCreateParams(
       self.browser->browser_state());
   std::unique_ptr<web::WebState> webState =
       web::WebState::Create(webStateCreateParams);
   self.webStateList.InsertWebState(self.webStateList.count(),
-                                   webState.release(), nullptr);
+                                   webState.release());
   [self showTabAtIndex:self.webStateList.count() - 1];
 }
 
 #pragma mark - TabGridCommands
 
 - (void)showTabGrid {
   // This object should only ever have at most one child.
   DCHECK_LE(self.children.count, 1UL);
   BrowserCoordinator* child = [self.children anyObject];
   [child stop];
@@ skipping 28 matching lines @@
   web::WebState* activeWebState = self.webStateList.GetActiveWebState();
   web::NavigationManager::WebLoadParams params(net::GURLWithNSURL(URL));
   params.transition_type = ui::PAGE_TRANSITION_LINK;
   activeWebState->GetNavigationManager()->LoadURLWithParams(params);
   if (!self.children.count) {
     [self showTabAtIndex:self.webStateList.active_index()];
   }
 }
 
 @end