Fix ios_chrome_unittests to crash on DCHECK failure.

ios/chrome/browser/crash_loop_detection_util.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 "ios/chrome/browser/crash_loop_detection_util.h"
 
 #import <Foundation/Foundation.h>
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #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];
   }
   return startup_attempt_count;
 }
 
 void IncrementFailedStartupAttemptCount(bool flush_immediately) {
   int startup_attempt_count = GetFailedStartupAttemptCount();
   NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
   [defaults setInteger:(startup_attempt_count + 1)
                 forKey:kAppStartupFailureCountKey];
   if (flush_immediately)
     [defaults synchronize];
 }
 
 void ResetFailedStartupAttemptCount() {
   NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
   if ([defaults integerForKey:kAppStartupFailureCountKey] != 0) {
     [defaults setInteger:0 forKey:kAppStartupFailureCountKey];
     [defaults synchronize];
   }
 }
 
+void ResetFailedStartupAttemptCountForTests() {
+  ResetFailedStartupAttemptCount();
+  startup_attempt_count = -1;
+}
+
 }  // namespace crash_util