[ObjC ARC] Converts ios/chrome/app/safe_mode:safe_mode to ARC.

ios/chrome/app/safe_mode/safe_mode_coordinator.h

 // Copyright 2016 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_APP_SAFE_MODE_SAFE_MODE_COORDINATOR_H_
 #define IOS_CHROME_APP_SAFE_MODE_SAFE_MODE_COORDINATOR_H_
 
 #import "ios/chrome/browser/chrome_root_coordinator.h"
 
 #import <UIKit/UIKit.h>
 
 @class SafeModeCoordinator;
 
 @protocol SafeModeCoordinatorDelegate<NSObject>
 - (void)coordinatorDidExitSafeMode:(nonnull SafeModeCoordinator*)coordinator;
 @end
 
 // Coordinator to manage the Safe Mode UI. This should be self-contained.
 // While this is a ChromeCoordinator, it doesn't support (and will DCHECK) using
 // child coordinators.
 @interface SafeModeCoordinator : ChromeRootCoordinator
 
 // Delegate for this coordinator.
-@property(nonatomic, nullable, assign) id<SafeModeCoordinatorDelegate> delegate;
+@property(nonatomic, nullable, weak) id<SafeModeCoordinatorDelegate> delegate;
 
 // If YES, there's a reason to show this coordinator.
 + (BOOL)shouldStart;
 
 @end
 
 #endif  // IOS_CHROME_APP_SAFE_MODE_SAFE_MODE_COORDINATOR_H_