Added NavigationManager::GetIndexOfItem().

ios/web/navigation/navigation_manager_impl.mm

 // Copyright 2013 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/web/navigation/navigation_manager_impl.h"
 
 #include <stddef.h>
 
 #include <utility>
 
@@ skipping 249 matching lines @@
 }
 
 int NavigationManagerImpl::GetItemCount() const {
   return [session_controller_ items].size();
 }
 
 NavigationItem* NavigationManagerImpl::GetItemAtIndex(size_t index) const {
   return [session_controller_ itemAtIndex:index];
 }
 
+int NavigationManagerImpl::GetIndexOfItem(
+    const web::NavigationItem* item) const {
+  return [session_controller_ indexOfItem:item];
+}
+
 int NavigationManagerImpl::GetPendingItemIndex() const {
   if (GetPendingItem()) {
     if ([session_controller_ pendingItemIndex] != -1) {
       return [session_controller_ pendingItemIndex];
     }
     // TODO(crbug.com/665189): understand why last committed item index is
     // returned here.
     return GetLastCommittedItemIndex();
   }
   return -1;
@@ skipping 163 matching lines @@
   const ScopedNavigationItemImplList& items = [session_controller_ items];
   while (index >= 0) {
     NavigationItem* item = items[index--].get();
     if (!client->IsAppSpecificURL(item->GetVirtualURL()))
       return item;
   }
   return nullptr;
 }
 
 }  // namespace web