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

ios/chrome/browser/crash_loop_detection_util_unittest.mm

 // Copyright 2013 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 <Foundation/Foundation.h>
 
 #include "ios/chrome/browser/crash_loop_detection_util.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/platform_test.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 // The key used to store the count in the implementation.
 NSString* const kAppStartupAttemptCountKey = @"AppStartupFailureCount";
 
 typedef PlatformTest CrashLoopDetectionUtilTest;
 
 TEST_F(CrashLoopDetectionUtilTest, FullCycle) {
   crash_util::ResetFailedStartupAttemptCountForTests();
 
   // Simulate one prior crash.
@@ skipping 14 matching lines @@
   crash_util::IncrementFailedStartupAttemptCount(false);
   EXPECT_EQ(2, [defaults integerForKey:kAppStartupAttemptCountKey]);
 
   // After a reset it should be 0 internally, but the same via the API.
   crash_util::ResetFailedStartupAttemptCount();
   EXPECT_EQ(1, crash_util::GetFailedStartupAttemptCount());
   EXPECT_EQ(0, [defaults integerForKey:kAppStartupAttemptCountKey]);
 }
 
 }  // namespace