[iOS] Upstream crash loop detection utilities

ios/chrome/browser/crash_loop_detection_util.h

+// 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.
+
+#ifndef IOS_CHROME_BROWSER_CRASH_LOOP_DETECTION_UTIL_H_
+#define IOS_CHROME_BROWSER_CRASH_LOOP_DETECTION_UTIL_H_
+
+namespace crash_util {
+
+// Returns the number of consecutive failed startups ('instant' crashes) prior
+// to this one. This method always returns the number of prior failures even
+// after calls to increment or reset the value.
+int GetFailedStartupAttemptCount();
+
+// Increases the failed startup count. This should be called immediately after
+// startup, so that if there is a crash, it is recorded.
+// If |flush_immediately| is true, the value will be persisted immediately. If
+// |flush_immediately| is false, this should be followed by a call to
+// [[NSUserDefaults standardUserDefaults] synchronize]. This is optional to
+// allow coallescing of the potentially expensive call during startup.
+void IncrementFailedStartupAttemptCount(bool flush_immediately);
+
+// Resets the failed startup count. This should be called once there is some
+// indication the user isn't in a crash loop (e.g., some amount of time has
+// elapsed, or some deliberate user action has been taken).
+void ResetFailedStartupAttemptCount();
+
+}  // namespace crash_util
+
+#endif  // IOS_CHROME_BROWSER_CRASH_LOOP_DETECTION_UTIL_H_