Fix crash in web workers when entangled port sender is null.

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/browser_thread.h"
 #include "chrome/browser/renderer_host/resource_message_filter.h"
@@ skipping 177 matching lines @@
     // send along with the message.
     std::vector<int> new_routing_ids(sent_message_port_ids.size());
     for (size_t i = 0; i < sent_message_port_ids.size(); ++i) {
       new_routing_ids[i] = entangled_port.next_routing_id->Run();
       sent_ports[i]->sender = entangled_port.sender;
 
       // Update the entry for the sent port as it can be in a different process.
       sent_ports[i]->route_id = new_routing_ids[i];
     }
 
-    // Now send the message to the entangled port.
-    IPC::Message* ipc_msg = new WorkerProcessMsg_Message(
-        entangled_port.route_id, message, sent_message_port_ids,
-        new_routing_ids);
-    entangled_port.sender->Send(ipc_msg);
+    if (entangled_port.sender) {
+      // Now send the message to the entangled port.
+      IPC::Message* ipc_msg = new WorkerProcessMsg_Message(
+          entangled_port.route_id, message, sent_message_port_ids,
+          new_routing_ids);
+      entangled_port.sender->Send(ipc_msg);
+    }
   }
 }
 
 void MessagePortDispatcher::OnQueueMessages(int message_port_id) {
   if (!message_ports_.count(message_port_id)) {
     NOTREACHED();
     return;
   }
 
   MessagePort& port = message_ports_[message_port_id];
-  port.sender->Send(new WorkerProcessMsg_MessagesQueued(port.route_id));
-  port.queue_messages = true;
-  port.sender = NULL;
+  if (port.sender) {
+    port.sender->Send(new WorkerProcessMsg_MessagesQueued(port.route_id));
+    port.queue_messages = true;
+    port.sender = NULL;
+  }
 }
 
 void MessagePortDispatcher::OnSendQueuedMessages(
     int message_port_id,
     const QueuedMessages& queued_messages) {
   if (!message_ports_.count(message_port_id)) {
     NOTREACHED();
     return;
   }
 
@@ skipping 53 matching lines @@
   int entangled_id = erase_item->second.entangled_message_port_id;
   if (entangled_id != MSG_ROUTING_NONE) {
     // Do the disentanglement (and be paranoid about the other side existing
     // just in case something unusual happened during entanglement).
     if (message_ports_.count(entangled_id)) {
       message_ports_[entangled_id].entangled_message_port_id = MSG_ROUTING_NONE;
     }
   }
   message_ports_.erase(erase_item);
 }