Allow CollectionViewModel/Controller queries without SectionIdentifier

ios/chrome/browser/ui/collection_view/collection_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.
 
 #import "ios/chrome/browser/ui/collection_view/collection_view_controller.h"
 
 #include "base/logging.h"
 #include "base/mac/foundation_util.h"
 #import "ios/chrome/browser/ui/collection_view/cells/collection_view_item.h"
 #import "ios/chrome/browser/ui/collection_view/collection_view_model.h"
@@ skipping 53 matching lines @@
 - (void)reconfigureCellsForItems:(NSArray*)items
          inSectionWithIdentifier:(NSInteger)sectionIdentifier {
   for (CollectionViewItem* item in items) {
     NSIndexPath* indexPath =
         [self.collectionViewModel indexPathForItem:item
                            inSectionWithIdentifier:sectionIdentifier];
     [self reconfigureCellAtIndexPath:indexPath withItem:item];
   }
 }
 
+- (void)reconfigureCellsForItems:(NSArray*)items {
+  for (CollectionViewItem* item in items) {
+    NSIndexPath* indexPath = [self.collectionViewModel indexPathForItem:item];
+    [self reconfigureCellAtIndexPath:indexPath withItem:item];
+  }
+}
+
 - (void)reconfigureCellsAtIndexPaths:(NSArray*)indexPaths {
   for (NSIndexPath* indexPath in indexPaths) {
     CollectionViewItem* item =
         [self.collectionViewModel itemAtIndexPath:indexPath];
     [self reconfigureCellAtIndexPath:indexPath withItem:item];
   }
 }
 
 #pragma mark MDCCollectionViewEditingDelegate
 
@@ skipping 187 matching lines @@
       base::mac::ObjCCastStrict<MDCCollectionViewCell>(
           [self.collectionView cellForItemAtIndexPath:indexPath]);
 
   // |cell| may be nil if the row is not currently on screen.
   if (cell) {
     [item configureCell:cell];
   }
 }
 
 @end