[CRD iOS] Use UINavigationController for view stack manipulation

remoting/ios/app/host_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/host_view_controller.h"
 
@@ skipping 240 matching lines @@
         currentInputMode == remoting::GestureInterpreter::DIRECT_INPUT_MODE
             ? remoting::GestureInterpreter::TRACKPAD_INPUT_MODE
             : remoting::GestureInterpreter::DIRECT_INPUT_MODE);
   };
   [alert addAction:[UIAlertAction actionWithTitle:switchInputModeTitle
                                             style:UIAlertActionStyleDefault
                                           handler:switchInputModeHandler]];
 
   void (^disconnectHandler)(UIAlertAction*) = ^(UIAlertAction*) {
     [_client disconnectFromHost];
-    [self dismissViewControllerAnimated:YES completion:nil];
+    [self.navigationController popViewControllerAnimated:YES];
   };
   [alert addAction:[UIAlertAction actionWithTitle:@"Disconnect"
                                             style:UIAlertActionStyleDefault
                                           handler:disconnectHandler]];
 
   void (^cancelHandler)(UIAlertAction*) = ^(UIAlertAction*) {
     [alert dismissViewControllerAnimated:YES completion:nil];
   };
   [alert addAction:[UIAlertAction actionWithTitle:@"Cancel"
                                             style:UIAlertActionStyleCancel
                                           handler:cancelHandler]];
 
   alert.popoverPresentationController.sourceView = self.view;
   // Target the alert menu at the top middle of the FAB.
   alert.popoverPresentationController.sourceRect = CGRectMake(
       _floatingButton.center.x, _floatingButton.frame.origin.y, 1.0, 1.0);
 
   alert.popoverPresentationController.permittedArrowDirections =
       UIPopoverArrowDirectionDown;
   [self presentViewController:alert animated:YES completion:nil];
 }
 
 @end