Allow CollectionViewModel/Controller queries without SectionIdentifier

ios/chrome/browser/ui/authentication/signin_account_selector_view_controller.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.
 
 #include "ios/chrome/browser/ui/authentication/signin_account_selector_view_controller.h"
 
 #include <memory>
 
 #import "base/mac/foundation_util.h"
 #import "base/mac/scoped_nsobject.h"
@@ skipping 226 matching lines @@
     NSArray* accountItems = [self.collectionViewModel
         itemsInSectionWithIdentifier:SectionIdentifierAccounts];
     for (CollectionViewAccountItem* accountItem in accountItems) {
       if (accountItem != selectedAccountItem &&
           accountItem.accessoryType != MDCCollectionViewCellAccessoryNone) {
         // TODO(crbug.com/631486) : Checkmark animation.
         accountItem.accessoryType = MDCCollectionViewCellAccessoryNone;
         [reloadItems addObject:accountItem];
       }
     }
-    [self reconfigureCellsForItems:reloadItems
-           inSectionWithIdentifier:SectionIdentifierAccounts];
+    [self reconfigureCellsForItems:reloadItems];
   } else if (item.type == ItemTypeAddAccount) {
     [self.delegate accountSelectorControllerDidSelectAddAccount:self];
   }
 }
 
 #pragma mark - ChromeIdentityServiceObserver
 
 - (void)onIdentityListChanged {
   ChromeIdentity* selectedIdentity = [self selectedIdentity];
   [self loadModel];
@@ skipping 65 matching lines @@
       [self.collectionViewModel itemTypeForIndexPath:indexPath];
   return (itemType == ItemTypeTitle);
 }
 
 - (BOOL)collectionView:(nonnull UICollectionView*)collectionView
     shouldHideItemBackgroundAtIndexPath:(nonnull NSIndexPath*)indexPath {
   return YES;
 }
 
 @end