Fix crash when updating UITableViewCells in iOS 12

In iOS 12, calling
[UITableView reloadRowsAtIndexPaths:withRowAnimation:] inside the
completion handler of [UITableView performBatchUpdates:completion:] may
trigger a crash.

The workaround is to get UITableViewCell via
[UITableView cellForRowAtIndexPath:] and then reconfigure the cell
directly. This will lose the built-in animation from UIKit when cells
are updated.

Once iOS 12 is deprecated, remove this workaround and use
[UITableView reloadRowsAtIndexPaths:withRowAnimation:].

Bug: 1028074
Change-Id: Ida4fbf94f31b7b00cb9052177f3350c60ae9e4e2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1936487Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Yi Su <mrsuyi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#719135}

ios/chrome/browser/ui/settings/search_engine_table_view_controller.mm

@@ -522,9 +522,26 @@ const char kUmaSelectDefaultSearchEngine[] =
     } else {
       engineItem.accessoryType = UITableViewCellAccessoryNone;
     }
+
+    // This function might be called inside the completion handler of
+    // [UITableView performBatchUpdates:completion:], which will cause a crash
+    // in iOS 12.
+    // TODO(crbug.com/1028546): Remove this workaround once iOS 12 is
+    // deprecated.
+    if (@available(iOS 13, *)) {
+    } else {
+      UITableViewCell* cell = [self.tableView cellForRowAtIndexPath:indexPath];
+      if (cell) {
+        TableViewCell* tableViewCell =
+            base::mac::ObjCCastStrict<TableViewCell>(cell);
+        [item configureCell:tableViewCell withStyler:self.styler];
+      }
+    }
+  }
+  if (@available(iOS 13, *)) {
+    [self.tableView reloadRowsAtIndexPaths:indexPaths
+                          withRowAnimation:UITableViewRowAnimationAutomatic];
   }
-  [self.tableView reloadRowsAtIndexPaths:indexPaths
-                        withRowAnimation:UITableViewRowAnimationAutomatic];
 }
 
 @end