[ios] Take snapshot for tab grid.

ios/clean/chrome/browser/ui/tab_collection/tab_collection_tab_cell.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/clean/chrome/browser/ui/tab_collection/tab_collection_tab_cell.h"
 
 #import "ios/chrome/browser/snapshots/snapshot_cache.h"
 #import "ios/chrome/browser/ui/tab_switcher/tab_switcher_button.h"
 #import "ios/chrome/browser/ui/uikit_ui_util.h"
 #include "ios/chrome/grit/ios_theme_resources.h"
@@ skipping 46 matching lines @@
   self.snapshotButton.accessibilityIdentifier =
       [NSString stringWithFormat:@"%@_button", item.title];
   self.contentView.accessibilityLabel = item.title;
   self.favicon.image = NativeImage(IDR_IOS_OMNIBOX_HTTP);
   __weak TabCollectionTabCell* weakSelf = self;
   [snapshotCache
       retrieveImageForSessionID:self.item.tabID
                        callback:^(UIImage* snapshot) {
                          // PLACEHOLDER: This operation will be cancellable.
                          if ([weakSelf.item.tabID isEqualToString:item.tabID]) {
-                           [weakSelf setSnapshot:snapshot];
+                           weakSelf.snapshot = snapshot;
                          }
                        }];
 }
 
 #pragma mark - Private methods
 
 - (void)setupSelectedBackgroundView {
   self.selectedBackgroundView = [[UIView alloc] init];
   self.selectedBackgroundView.backgroundColor = [UIColor blackColor];
 
@@ skipping 14 matching lines @@
     [border.trailingAnchor
         constraintEqualToAnchor:self.selectedBackgroundView.trailingAnchor
                        constant:kBorderMargin],
     [border.bottomAnchor
         constraintEqualToAnchor:self.selectedBackgroundView.bottomAnchor
                        constant:kBorderMargin]
   ]];
 }
 
 @end