Remove the concept of currentItemIndex

ios/shared/chrome/browser/tabs/web_state_list.mm

 // 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.
 
 #import "ios/shared/chrome/browser/tabs/web_state_list.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/logging.h"
@@ skipping 283 matching lines @@
 
 int WebStateList::GetIndexOfNthWebStateOpenedBy(const web::WebState* opener,
                                                 int start_index,
                                                 bool use_group,
                                                 int n) const {
   DCHECK_GT(n, 0);
   if (!opener || !ContainsIndex(start_index) || start_index == INT_MAX)
     return kInvalidIndex;
 
   const int opener_navigation_index =
-      use_group ? opener->GetNavigationManager()->GetCurrentItemIndex() : -1;
+      use_group ? opener->GetNavigationManager()->GetLastCommittedItemIndex()
+                : -1;
 
   int found_index = kInvalidIndex;
   for (int index = start_index + 1; index < count() && n; ++index) {
     if (web_state_wrappers_[index]->WasOpenedBy(opener, opener_navigation_index,
                                                 use_group)) {
       found_index = index;
       --n;
     } else if (found_index != kInvalidIndex) {
       return found_index;
     }
   }
 
   return found_index;
 }
 
 // static
 const int WebStateList::kInvalidIndex;