[ObjC ARC] Converts ios/chrome/browser/ui/ntp:unit_tests to ARC.

ios/chrome/browser/ui/ntp/most_visited_cell_unittest.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.
 
-#include "base/mac/scoped_nsobject.h"
 #import "ios/chrome/browser/ui/ntp/most_visited_cell.h"
 #include "testing/platform_test.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 static NSString* title = @"Most Visited Cell Title";
 const GURL URL = GURL("http://example.com");
 
 // Fixture to test MostVisitedCell.
 class MostVisitedCellTest : public PlatformTest {
  protected:
-  base::scoped_nsobject<MostVisitedCell> cell_;
+  MostVisitedCell* cell_;
 };
 
 TEST_F(MostVisitedCellTest, TestConstructor) {
   CGRect rect = CGRectMake(0, 0, 100, 100);
-  cell_.reset([[MostVisitedCell alloc] initWithFrame:rect]);
+  cell_ = [[MostVisitedCell alloc] initWithFrame:rect];
   [cell_ setURL:URL];
-  EXPECT_TRUE(cell_.get());
+  EXPECT_TRUE(cell_);
   UIGraphicsBeginImageContext([cell_ bounds].size);
   [cell_ drawRect:[cell_ bounds]];
   UIGraphicsEndImageContext();
   EXPECT_EQ(URL, [cell_ URL]);
 }
 
 TEST_F(MostVisitedCellTest, ValidateTitle) {
   CGRect rect = CGRectMake(0, 0, 100, 100);
-  cell_.reset([[MostVisitedCell alloc] initWithFrame:rect]);
+  cell_ = [[MostVisitedCell alloc] initWithFrame:rect];
   [cell_ setText:title];
   EXPECT_EQ(title, [cell_ accessibilityLabel]);
 }