Allow CollectionViewModel/Controller queries without SectionIdentifier

ios/chrome/browser/ui/collection_view/collection_view_model.mm

Index: ios/chrome/browser/ui/collection_view/collection_view_model.mm
diff --git a/ios/chrome/browser/ui/collection_view/collection_view_model.mm b/ios/chrome/browser/ui/collection_view/collection_view_model.mm
index 0866b37bdafde7636ef71ab9c88f608417224f14..460091ffc9a7435bbbc74e89834abac1689c72fa 100644
--- a/ios/chrome/browser/ui/collection_view/collection_view_model.mm
+++ b/ios/chrome/browser/ui/collection_view/collection_view_model.mm
@@ -267,6 +267,25 @@ typedef NSMutableArray<CollectionViewItem*> SectionItems;
   return [NSIndexPath indexPathForItem:itemIndex inSection:section];
 }
 
+- (BOOL)hasItem:(CollectionViewItem*)item {
+  for (SectionItems* sectionItems in _sections) {

[lpromero, 2017/03/28 09:09:08]

Iterate on _sectionIdentifiers and use haseItem:inSectionWithIdentifier:.

[gambard, 2017/03/28 13:35:22]

I wanted to offer a solution without the current implementation in case we
wanted to remove the current implementation.
Done.

+    if ([sectionItems indexOfObject:item] != NSNotFound)
+      return YES;
+  }
+  return NO;
+}
+
+- (NSIndexPath*)indexPathForItem:(CollectionViewItem*)item {
+  for (NSUInteger section = 0; section < [_sections count]; section++) {

[lpromero, 2017/03/28 09:09:08]

Idem, use the same methods that use the sectionIdentifier.

[gambard, 2017/03/28 13:35:22]

This method was slightly more efficient (lookup only once in the section
containing the item).
Done anyway.

+    NSInteger itemIndex = [_sections[section] indexOfObject:item];
+    if (itemIndex != NSNotFound) {
+      return [NSIndexPath indexPathForItem:itemIndex inSection:section];
+    }
+  }
+  DCHECK(NO);

[lpromero, 2017/03/28 09:09:08]

Use NOTREACHED().

[gambard, 2017/03/28 13:35:22]

Done.

+  return nil;
+}
+
 #pragma mark UICollectionView data sourcing
 
 - (NSInteger)numberOfSections {