Use ARC for Suggestions tests

ios/chrome/browser/ui/suggestions/suggestions_expandable_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_expandable_item.h"
 
-#import "ios/chrome/browser/ui/collection_view/cells/collection_view_item.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #import "third_party/ocmock/OCMock/OCMock.h"
 #include "third_party/ocmock/gtest_support.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 // Test subclass of the SuggestionsExpandableCell.
 @interface TestSuggestionsExpandableCell : SuggestionsExpandableCell
 
 @property(nonatomic) BOOL expandCalled;
 @property(nonatomic) BOOL collapseCalled;
 
 @end
 
 @implementation TestSuggestionsExpandableCell
 
@@ skipping 73 matching lines @@
       [[TestSuggestionsExpandableCell alloc] init];
   item.cellClass = [TestSuggestionsExpandableCell class];
 
   item.expanded = NO;
   [item configureCell:cell];
   ASSERT_TRUE(cell.collapseCalled);
   ASSERT_FALSE(cell.expandCalled);
 }
 
 }  // namespace