Use ARC for Suggestions tests

ios/chrome/browser/ui/suggestions/suggestions_article_item_unittest.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/chrome/browser/ui/suggestions/suggestions_article_item.h"
 
-#import "ios/chrome/browser/ui/collection_view/cells/collection_view_item.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
+// Tests that configureCell: set all the fields of the cell.
 TEST(SuggestionsArticleItemTest, CellIsConfigured) {
   NSString* title = @"testTitle";
   NSString* subtitle = @"testSubtitle";
   UIImage* image = [[UIImage alloc] init];
   SuggestionsArticleItem* item =
       [[SuggestionsArticleItem alloc] initWithType:0
                                              title:title
                                           subtitle:subtitle
                                              image:image];
   SuggestionsArticleCell* cell = [[[item cellClass] alloc] init];
   EXPECT_TRUE([cell isMemberOfClass:[SuggestionsArticleCell class]]);
 
   [item configureCell:cell];
   EXPECT_EQ(title, cell.titleLabel.text);
   EXPECT_EQ(subtitle, cell.subtitleLabel.text);
   EXPECT_EQ(image, cell.imageView.image);
 }
 
 }  // namespace