[ObjC ARC] Converts ios/chrome/test/base:perf_test_support to ARC.

ios/chrome/test/base/perf_test_ios.mm

 // Copyright (c) 2012 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/logging.h"
 #include "base/memory/ptr_util.h"
 #import "ios/chrome/browser/web/chrome_web_client.h"
 #import "ios/chrome/test/base/perf_test_ios.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 PerfTest::PerfTest(std::string testGroup)
     : BlockCleanupTest(),
       testGroup_(testGroup),
       firstLabel_("1st"),
       averageLabel_("2nd+"),
       isWaterfall_(false),
       verbose_(true),
       repeatCount_(10),
       web_client_(base::MakeUnique<ChromeWebClient>()) {}
 PerfTest::PerfTest(std::string testGroup,
@@ skipping 83 matching lines @@
       max = times[i];
     if (times[i] < min)
       min = times[i];
   }
   if (max_time)
     *max_time = max;
   if (min_time)
     *min_time = min;
   return sum / count;
 }