[ObjC ARC] Converts ios/chrome/browser/ui/alert_coordinator:alert_coordinator to ARC.

ios/chrome/browser/ui/alert_coordinator/action_sheet_coordinator.mm

 // 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.
 
 #import "ios/chrome/browser/ui/alert_coordinator/action_sheet_coordinator.h"
 
-#import "base/mac/scoped_nsobject.h"
+#import "base/logging.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
 
 @interface ActionSheetCoordinator () {
   // Rectangle for the popover alert.
   CGRect _rect;
   // View for the popovert alert.
-  base::scoped_nsobject<UIView> _view;
+  UIView* _view;
 }
 
 @end
 
 @implementation ActionSheetCoordinator
 
 - (instancetype)initWithBaseViewController:(UIViewController*)viewController
                                      title:(NSString*)title
                                    message:(NSString*)message {
   NOTREACHED();
   return nil;
 }
 
 - (instancetype)initWithBaseViewController:(UIViewController*)viewController
                                      title:(NSString*)title
                                    message:(NSString*)message
                                       rect:(CGRect)rect
                                       view:(UIView*)view {
   self = [super initWithBaseViewController:viewController
                                      title:title
                                    message:message];
   if (self) {
     _rect = rect;
-    _view.reset([view retain]);
+    _view = view;
   }
   return self;
 }
 
 - (UIAlertController*)alertControllerWithTitle:(NSString*)title
                                        message:(NSString*)message {
   UIAlertController* alert = [UIAlertController
       alertControllerWithTitle:title
                        message:message
                 preferredStyle:UIAlertControllerStyleActionSheet];
 
   alert.popoverPresentationController.sourceView = _view;
   alert.popoverPresentationController.sourceRect = _rect;
 
   return alert;
 }
 
 @end