[tab_grid] Hack-in close tab.

ios/clean/chrome/browser/ui/tab_grid/tab_grid_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.
 
 // ======                        New Architecture                         =====
 // =         This code is only used in the new iOS Chrome architecture.       =
 // ============================================================================
 
 #import "ios/clean/chrome/browser/ui/tab_grid/tab_grid_view_controller.h"
 
@@ skipping 139 matching lines @@
 - (TabSwitcherCache*)tabSwitcherCache {
   // PLACEHOLDER: return image cache.
   return nil;
 }
 
 - (void)cellPressed:(UICollectionViewCell*)cell {
   [self.tabCommandHandler showTabAtIndexPath:[self.grid indexPathForCell:cell]];
 }
 
 - (void)deleteButtonPressedForCell:(UICollectionViewCell*)cell {
-  // PLACEHOLDER: handle close tab button.
+  auto updateBlock = ^{
+    NSIndexPath* indexPath = [self.grid indexPathForCell:cell];
+    [self.tabCommandHandler closeTabAtIndexPath:indexPath];
+    [self.grid deleteItemsAtIndexPaths:@[ indexPath ]];
+  };
+  [self.grid performBatchUpdates:updateBlock completion:nil];
 }
 
 @end