Fix ios_chrome_unittests to crash on DCHECK failure.

ios/chrome/browser/crash_loop_detection_util.mm

Index: ios/chrome/browser/crash_loop_detection_util.mm
diff --git a/ios/chrome/browser/crash_loop_detection_util.mm b/ios/chrome/browser/crash_loop_detection_util.mm
index 2eb1913a59098e684fb53d01931759728096c5cf..0de92d6c2b1d2e615c3b6d55fc4d54c9d11d3284 100644
--- a/ios/chrome/browser/crash_loop_detection_util.mm
+++ b/ios/chrome/browser/crash_loop_detection_util.mm
@@ -11,13 +11,13 @@
 #endif
 
 namespace {
+static int startup_attempt_count = -1;
 NSString* const kAppStartupFailureCountKey = @"AppStartupFailureCount";
 }
 
 namespace crash_util {
 
 int GetFailedStartupAttemptCount() {
-  static int startup_attempt_count = -1;
   if (startup_attempt_count == -1) {
     NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
     startup_attempt_count = [defaults integerForKey:kAppStartupFailureCountKey];
@@ -42,4 +42,9 @@ void ResetFailedStartupAttemptCount() {
   }
 }
 
+void ResetFailedStartupAttemptCountForTests() {
+  ResetFailedStartupAttemptCount();
+  startup_attempt_count = -1;
+}
+
 }  // namespace crash_util