Fix browser process crash in WorkerTest.WorkerContextMultiPort.

chrome/browser/worker_host/message_port_dispatcher.cc

 // Copyright (c) 2009 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 "chrome/browser/worker_host/message_port_dispatcher.h"
 
 #include "base/callback.h"
 #include "base/singleton.h"
 #include "chrome/browser/chrome_thread.h"
 #include "chrome/browser/renderer_host/resource_message_filter.h"
@@ skipping 219 matching lines @@
   port.queue_messages = false;
   port.queued_messages.insert(port.queued_messages.begin(),
                               queued_messages.begin(),
                               queued_messages.end());
   SendQueuedMessagesIfPossible(message_port_id);
   DCHECK(CheckMessagePortMap(true));
 }
 
 void MessagePortDispatcher::SendQueuedMessagesIfPossible(int message_port_id) {
   DCHECK(CheckMessagePortMap(true));
+  if (!message_ports_.count(message_port_id)) {
+    NOTREACHED();
+    return;
+  }
+
   MessagePort& port = message_ports_[message_port_id];
   if (port.queue_messages || !port.sender)
     return;
 
   for (QueuedMessages::iterator iter = port.queued_messages.begin();
        iter != port.queued_messages.end(); ++iter) {
     PostMessageTo(message_port_id, iter->first, iter->second);
   }
   port.queued_messages.clear();
   DCHECK(CheckMessagePortMap(true));
@@ skipping 52 matching lines @@
     int entangled_id = iter->second.entangled_message_port_id;
     if (check_entanglements && entangled_id != MSG_ROUTING_NONE) {
       MessagePorts::iterator entangled_item = message_ports_.find(entangled_id);
       DCHECK(entangled_item != message_ports_.end());
       DCHECK(entangled_item->second.entangled_message_port_id == iter->first);
     }
   }
   return true;
 }
 #endif  // NDEBUG