Hides the ink using dedicated method

To hide the ink on the empty items, ContentSuggestions was using a
transparent color for the ink instead of not starting the animation due
to an MDC bug. As the bug is fixed, the correct method can be used.

Bug: 724493
Change-Id: Id4a63ddcc9977b9c017f882bcf17c2a026ee13b2
Reviewed-on: https://chromium-review.googlesource.com/663340Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501300}

ios/chrome/browser/ui/content_suggestions/content_suggestions_view_controller.mm

@@ -435,18 +435,13 @@ BOOL ShouldCellsBeFullWidth(UITraitCollection* collection) {
 
 #pragma mark - MDCCollectionViewStylingDelegate
 
-// TODO(crbug.com/724493): Use collectionView:hidesInkViewAtIndexPath: when it
-// is fixed. For now hidding the ink prevent cell interaction.
-- (UIColor*)collectionView:(UICollectionView*)collectionView
-       inkColorAtIndexPath:(NSIndexPath*)indexPath {
+- (BOOL)collectionView:(UICollectionView*)collectionView
+    hidesInkViewAtIndexPath:(NSIndexPath*)indexPath {
   ContentSuggestionType itemType = [self.collectionUpdater
       contentSuggestionTypeForItem:[self.collectionViewModel
                                        itemAtIndexPath:indexPath]];
-  if ([self.collectionUpdater isMostVisitedSection:indexPath.section] ||
-      itemType == ContentSuggestionTypeEmpty) {
-    return [UIColor clearColor];
-  }
-  return nil;
+  return [self.collectionUpdater isMostVisitedSection:indexPath.section] ||
+         itemType == ContentSuggestionTypeEmpty;
 }
 
 - (UIColor*)collectionView:(nonnull UICollectionView*)collectionView