[iOS] Replace all instances of MDCSnackbarManager.showMessage.

Follow-up to patch 2362248 that migrates all instances of the deprecated
'showMesage:' method to [MDCSnackbarManager.defaultManager showMessage:]
in the Chrome remoting codebase.

TBR=yuweih@chromium.org

Bug: 1117399
Change-Id: I2e777c7759d7a16b51f989a225526dff94dfce87
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2363752Reviewed-by: Nohemi Fernandez <fernandex@chromium.org>
Commit-Queue: Nohemi Fernandez <fernandex@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799560}

remoting/ios/app/client_connection_view_controller.mm

@@ -626,7 +626,7 @@ using EntryPoint = remoting::ChromotingEvent::SessionEntryPoint;
       // If the session is closed by the host, just go back to the host list and
       // show a toast.
       state = ClientViewClosed;
-      [MDCSnackbarManager
+      [MDCSnackbarManager.defaultManager
           showMessage:[MDCSnackbarMessage
                           messageWithText:l10n_util::GetNSString(
                                               IDS_MESSAGE_SESSION_FINISHED)]];

remoting/ios/app/remoting_view_controller.mm

@@ -276,19 +276,20 @@ using remoting::HostListService;
   if (![cell.hostInfo isOnline]) {
     MDCSnackbarMessage* message = [[MDCSnackbarMessage alloc] init];
     message.text = l10n_util::GetNSString(IDS_HOST_OFFLINE_TOOLTIP);
-    [MDCSnackbarManager showMessage:message];
+    [MDCSnackbarManager.defaultManager showMessage:message];
     return;
   }
 
   if (GetConnectionType() == ConnectionType::NONE) {
-    [MDCSnackbarManager
+    [MDCSnackbarManager.defaultManager
         showMessage:[MDCSnackbarMessage
                         messageWithText:l10n_util::GetNSString(
                                             IDS_ERROR_NETWORK_ERROR)]];
     return;
   }
 
-  [MDCSnackbarManager dismissAndCallCompletionBlocksWithCategory:nil];
+  [MDCSnackbarManager.defaultManager
+      dismissAndCallCompletionBlocksWithCategory:nil];
   ClientConnectionViewController* clientConnectionViewController =
       [[ClientConnectionViewController alloc] initWithHostInfo:cell.hostInfo];
   [self.navigationController pushViewController:clientConnectionViewController

remoting/ios/app/side_menu_items.mm

@@ -61,7 +61,7 @@ static NSString* const kFeedbackContext = @"SideMenuFeedbackContext";
                      NSString* message =
                          [NSString stringWithFormat:@"Using WebRTC: %s",
                                                     newValue ? "Yes" : "No"];
-                     [MDCSnackbarManager
+                     [MDCSnackbarManager.defaultManager
                          showMessage:[MDCSnackbarMessage
                                          messageWithText:message]];
                    }],

remoting/ios/app/user_status_presenter.mm

@@ -80,7 +80,7 @@
   MDCSnackbarMessage* message = [[MDCSnackbarMessage alloc] init];
   message.text = l10n_util::GetNSStringF(
       IDS_LOG_IN_ACCOUNT_DESCRIPTION, base::SysNSStringToUTF16(user.userEmail));
-  [MDCSnackbarManager showMessage:message];
+  [MDCSnackbarManager.defaultManager showMessage:message];
 }
 
 @end

remoting/ios/facade/remoting_oauth_authentication.mm

@@ -145,7 +145,7 @@ RemotingAuthenticationStatus oauthStatusToRemotingAuthenticationStatus(
     } else {
       LOG(ERROR) << "Failed to fetch access token from authorization code. ("
                  << status << ")";
-      [MDCSnackbarManager
+      [MDCSnackbarManager.defaultManager
           showMessage:
               [MDCSnackbarMessage
                   messageWithText:@"Authentication Failed. Please try again."]];