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

ios/chrome/browser/ui/history/history_util_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 "ios/chrome/browser/ui/history/history_util.h"
 
 #include <stdint.h>
 
 #include "base/macros.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/time/time.h"
 #include "ios/chrome/browser/ui/history/history_entry.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 struct TestResult {
   std::string url;
   int64_t hour_offset;  // Visit time in hours past the baseline time.
 };
 
 // Duplicates on the same day in the local timezone are removed, so set a
 // baseline time in local time.
 const base::Time baseline_time = base::Time::UnixEpoch().LocalMidnight();
@@ skipping 99 matching lines @@
     AddQueryResults(test_data, arraysize(test_data), &results);
     history::MergeDuplicateHistoryEntries(&results);
 
     ASSERT_EQ(2U, results.size());
     EXPECT_TRUE(ResultEquals(results[0], test_data[3]));
     EXPECT_TRUE(ResultEquals(results[1], test_data[1]));
     EXPECT_EQ(3u, results[0].all_timestamps.size());
     EXPECT_EQ(1u, results[1].all_timestamps.size());
   }
 }