[iOS] Upstream crash loop detection utilities

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.
+
+#include <Foundation/Foundation.h>
+
+#include "ios/chrome/browser/crash_loop_detection_util.h"
+#include "testing/gtest/include/gtest/gtest.h"
+#include "testing/platform_test.h"
+
+namespace {
+// The key used to store the count in the implementation.
+NSString* const kAppStartupAttemptCountKey = @"AppStartupFailureCount";
+
+typedef PlatformTest CrashLoopDetectionUtilTest;
+
+TEST_F(CrashLoopDetectionUtilTest, FullCycle) {
+  // Simulate one prior crash.
+  NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
+  [defaults setInteger:1 forKey:kAppStartupAttemptCountKey];
+
+  EXPECT_EQ(1, crash_util::GetFailedStartupAttemptCount());
+
+  crash_util::IncrementFailedStartupAttemptCount(false);
+
+  // It should still report 1, since it's reporting failures prior to this
+  // launch.
+  EXPECT_EQ(1, crash_util::GetFailedStartupAttemptCount());
+  // ... but under the hood the value should now be 2.
+  EXPECT_EQ(2, [defaults integerForKey:kAppStartupAttemptCountKey]);
+
+  // If it's mistakenly incerement again, nothing should change.
+  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