Fix hitting a DCHECK in FtpNetworkTransaction on extra responses.

net/ftp/ftp_network_transaction.cc

Index: net/ftp/ftp_network_transaction.cc
diff --git a/net/ftp/ftp_network_transaction.cc b/net/ftp/ftp_network_transaction.cc
index b34511fa1527419f37ca87b059dd02b2fa7040b1..b5efb077482b5f7680b0dc4f3e3e2e8c7910a014 100644
--- a/net/ftp/ftp_network_transaction.cc
+++ b/net/ftp/ftp_network_transaction.cc
@@ -417,7 +417,9 @@ int FtpNetworkTransaction::ProcessCtrlResponse() {
   }
 
   // We may get multiple responses for some commands,
-  // see http://crbug.com/18036.
+  // see http://crbug.com/18036. Consume all responses, regardless of whether
+  // they make sense. On unexpected responses, SendFtpCommand expects all data
+  // to have already been consumed, even when sending the QUIT command.

[mmenke, 2016/11/28 17:28:22]

Another option would be to skip that DCHECK in case of a quit message, which
would mean we wouldn't wait for the response for the quit command, but only if
we received 2 or more unexpected messages, which seems weird (We should either
always wait for the quit response or never do it, when we get bonus messages,
regardless of how many we get).

   while (ctrl_response_buffer_->ResponseAvailable() && rv == OK) {
     response = ctrl_response_buffer_->PopResponse();
 
@@ -430,7 +432,8 @@ int FtpNetworkTransaction::ProcessCtrlResponse() {
         break;
       default:
         // Multiple responses for other commands are invalid.
-        return Stop(ERR_INVALID_RESPONSE);
+        rv = Stop(ERR_INVALID_RESPONSE);

[eroman, 2016/11/28 17:51:24]

I am not sure I understand this code flow.

rv will be OK in every case except when the sent command was COMMAND_QUIT.
But maybe I am misunderstanding the role of Stop()

[mmenke, 2016/11/28 18:21:01]

Stop sets the next state to send the quit message, so multiple calls don't cause
problems.  If we've already sent a quit messages, it just returns the error
synchronously, and we exit the loop, but don't DCHECK, because we don't send the
quit message again.

+        break;
     }
   }