[CRD iOS] Don't attempt to connect to an offline host

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 185 matching lines @@
   if (_client) {
     return _client.hostInfo.hostName;
   }
   return nil;
 }
 
 #pragma mark - HostCollectionViewControllerDelegate
 
 - (void)didSelectCell:(HostCollectionViewCell*)cell
            completion:(void (^)())completionBlock {
+  if (![cell.hostInfo isOnline]) {
+    MDCSnackbarMessage* message = [[MDCSnackbarMessage alloc] init];
+    message.text = @"Host is offline.";

[nicholss, 2017/06/01 21:56:57]

Might be overkill but for now yeah, lets use it.

[Yuwei, 2017/06/01 22:06:49]

Okay. BTW this is what we do on Android #_#

+    [MDCSnackbarManager showMessage:message];
+    return;
+  }
+
   _client = [[RemotingClient alloc] init];
 
   [_remotingService.authentication
       callbackWithAccessToken:base::BindBlockArc(^(
                                   remoting::OAuthTokenGetter::Status status,
                                   const std::string& user_email,
                                   const std::string& access_token) {
         // TODO(nicholss): Check status.
         HostInfo* hostInfo = cell.hostInfo;
         [_client connectToHost:hostInfo
@@ skipping 72 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