[CRD iOS] Refactor an interface for RemotingAuthorization

remoting/ios/app/app_view_controller_chromium.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/app_view_controller.h"
 
 #include "base/logging.h"
 
 #import "remoting/ios/app/remoting_menu_view_controller.h"
+#import "remoting/ios/facade/remoting_oauth_authentication.h"
 
 // The Chromium implementation for the AppViewController. It simply shows the
 // menu modally.
 @interface AppViewController () {
-  UIViewController* _mainViewController;
 
   RemotingMenuViewController* _menuController;  // nullable
 }
 @end
 
 @implementation AppViewController
 
-- (instancetype)initWithMainViewController:
-    (UIViewController*)mainViewController {
+@synthesize authentication = _authentication;
+@synthesize mainViewController = _mainViewController;
+
+- (instancetype)init {
   if (self = [super init]) {
-    _mainViewController = mainViewController;
+    _authentication = [[RemotingOAuthAuthentication alloc] init];
   }
   return self;
 }
 
-- (void)viewDidLoad {
-  [self addChildViewController:_mainViewController];
-  [self.view addSubview:_mainViewController.view];
-  [_mainViewController didMoveToParentViewController:self];
-}
-
 #pragma mark - AppController
 - (void)showMenuAnimated:(BOOL)animated {
   if (_menuController != nil && [_menuController isBeingPresented]) {
     return;
   }
   _menuController = [[RemotingMenuViewController alloc] init];
   [self presentViewController:_menuController animated:animated completion:nil];
 }
 
 - (void)hideMenuAnimated:(BOOL)animated {
   if (_menuController == nil || ![_menuController isBeingPresented]) {
     return;
   }
   [_menuController dismissViewControllerAnimated:animated completion:nil];
   _menuController = nil;
 }
 
 - (void)presentSignInFlow {
   [self showMenuAnimated:YES];
 }
 
 - (UIViewController*)childViewControllerForStatusBarStyle {
   return _mainViewController;
 }
 
 - (UIViewController*)childViewControllerForStatusBarHidden {
   return _mainViewController;
 }
 
+#pragma mark - Properties
+
+- (void)setMainViewController:(UIViewController*)mainViewController {
+  DCHECK(self.view != nil);
+  _mainViewController = mainViewController;
+  [self addChildViewController:_mainViewController];
+  [self.view addSubview:_mainViewController.view];
+  [_mainViewController didMoveToParentViewController:self];
+}
+
 @end