Fix browser process crash in WorkerTest.WorkerContextMultiPort.

chrome/browser/worker_host/message_port_dispatcher.cc

Index: chrome/browser/worker_host/message_port_dispatcher.cc
diff --git a/chrome/browser/worker_host/message_port_dispatcher.cc b/chrome/browser/worker_host/message_port_dispatcher.cc
index f6e2bbf5c02e219b4ea1eb1b33f4dfa144a701ad..070ea3d6ba793d02a28efd1157fa11a8a267e996 100644
--- a/chrome/browser/worker_host/message_port_dispatcher.cc
+++ b/chrome/browser/worker_host/message_port_dispatcher.cc
@@ -237,6 +237,11 @@ void MessagePortDispatcher::OnSendQueuedMessages(
 
 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;