[ios] Take snapshot for tab grid.

ios/clean/chrome/browser/ui/tab_collection/tab_collection_view_controller.mm

 // Copyright 2017 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/clean/chrome/browser/ui/tab_collection/tab_collection_view_controller.h"
 
 #include "base/logging.h"
 #include "base/mac/foundation_util.h"
 #include "base/strings/sys_string_conversions.h"
 #import "ios/clean/chrome/browser/ui/tab_collection/tab_collection_item.h"
@@ skipping 139 matching lines @@
   DCHECK_LE(item, INT_MAX);
   int index = static_cast<int>(item);
   [self closeTabAtIndex:index];
 }
 
 #pragma mark - TabCollectionConsumer methods
 
 - (void)insertItem:(TabCollectionItem*)item
            atIndex:(int)index
      selectedIndex:(int)selectedIndex {
+  DCHECK(item);
   DCHECK_GE(index, 0);
   DCHECK_LE(static_cast<NSUInteger>(index), self.items.count);
   [self.items insertObject:item atIndex:index];
   [self.tabs insertItemsAtIndexPaths:@[ [NSIndexPath indexPathForItem:index
                                                             inSection:0] ]];
   self.selectedIndex = selectedIndex;
 }
 
 - (void)deleteItemAtIndex:(int)index selectedIndex:(int)selectedIndex {
   DCHECK_GE(index, 0);
@@ skipping 27 matching lines @@
   [cell configureCell:self.items[index] snapshotCache:self.snapshotCache];
 }
 
 - (void)populateItems:(NSArray<TabCollectionItem*>*)items
         selectedIndex:(int)selectedIndex {
   self.items = [items mutableCopy];
   [self.tabs reloadItemsAtIndexPaths:[self.tabs indexPathsForVisibleItems]];
   self.selectedIndex = selectedIndex;
 }
 
+- (void)updateSnapshotAtIndex:(int)index {
+  DCHECK_GE(index, 0);
+  DCHECK_LT(static_cast<NSUInteger>(index), self.items.count);
+  TabCollectionTabCell* cell = base::mac::ObjCCastStrict<TabCollectionTabCell>(
+      [self.tabs cellForItemAtIndexPath:[NSIndexPath indexPathForItem:index
+                                                            inSection:0]]);
+  [cell configureCell:self.items[index] snapshotCache:self.snapshotCache];
+}
+
 @end