[CRD iOS] Refactor an interface for RemotingAuthorization

remoting/ios/app/remoting_view_controller.mm

 // Copyright 2017 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.
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 #import "remoting/ios/app/remoting_view_controller.h"
 
@@ skipping 40 matching lines @@
   UICollectionViewFlowLayout* layout =
       [[MDCCollectionViewFlowLayout alloc] init];
   layout.minimumInteritemSpacing = 0;
   CGFloat sectionInset = kHostInset * 2.f;
   [layout setSectionInset:UIEdgeInsetsMake(sectionInset, sectionInset,
                                            sectionInset, sectionInset)];
   HostCollectionViewController* collectionVC = [
       [HostCollectionViewController alloc] initWithCollectionViewLayout:layout];
   self = [super initWithContentViewController:collectionVC];
   if (self) {
-    _remotingService = [RemotingService SharedInstance];
+    _remotingService = RemotingService.instance;
 
     _collectionViewController = collectionVC;
     _collectionViewController.flexHeaderContainerViewController = self;
     _collectionViewController.delegate = self;
 
     _appBar = [[MDCAppBar alloc] init];
     [self addChildViewController:_appBar.headerViewController];
 
     self.navigationItem.title = @"Chrome Remote Desktop";
 
@@ skipping 184 matching lines @@
   MDCSnackbarMessage* message = [[MDCSnackbarMessage alloc] init];
   if (_isAuthenticated) {
     message.text = [NSString
         stringWithFormat:@"Currently signed in as %@.",
                          _remotingService.authentication.user.userEmail];
     [MDCSnackbarManager showMessage:message];
   }
 }
 
 @end