[Extensions] DCHECK that ExtensionFunctions respond (and only once)

extensions/browser/api/sockets_udp/udp_socket_event_dispatcher.cc

 // Copyright 2014 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.
 
 #include "extensions/browser/api/sockets_udp/udp_socket_event_dispatcher.h"
 
 #include <utility>
 
 #include "base/lazy_instance.h"
 #include "extensions/browser/api/socket/udp_socket.h"
@@ skipping 117 matching lines @@
 
     // Post a task to delay the read until the socket is available, as
     // calling StartReceive at this point would error with ERR_IO_PENDING.
     BrowserThread::PostTask(
         params.thread_id,
         FROM_HERE,
         base::Bind(&UDPSocketEventDispatcher::StartReceive, params));
   } else if (bytes_read == net::ERR_IO_PENDING) {
     // This happens when resuming a socket which already had an
     // active "recv" callback.
+  } else if (bytes_read == net::ERR_CONNECTION_CLOSED) {
+    // This happens when the socket closes, which is expected since we
+    // continually add a receive listener in the success block above.
   } else {
     // Dispatch "onReceiveError" event but don't start another read to avoid
     // potential infinite reads if we have a persistent network error.
     sockets_udp::ReceiveErrorInfo receive_error_info;
     receive_error_info.socket_id = params.socket_id;
     receive_error_info.result_code = bytes_read;
     std::unique_ptr<base::ListValue> args =
         sockets_udp::OnReceiveError::Create(receive_error_info);
     std::unique_ptr<Event> event(
         new Event(events::SOCKETS_UDP_ON_RECEIVE_ERROR,
@@ skipping 31 matching lines @@
       reinterpret_cast<content::BrowserContext*>(browser_context_id);
   if (!extensions::ExtensionsBrowserClient::Get()->IsValidContext(context))
     return;
   EventRouter* router = EventRouter::Get(context);
   if (router)
     router->DispatchEventToExtension(extension_id, std::move(event));
 }
 
 }  // namespace api
 }  // namespace extensions