Try to fix a valgrind leak.

chrome/browser/extensions/extension_message_service.cc

 // Copyright (c) 2010 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/extensions/extension_message_service.h"
 
 #include "base/json/json_writer.h"
 #include "base/singleton.h"
 #include "base/stl_util-inl.h"
 #include "base/values.h"
@@ skipping 456 matching lines @@
   const MessagePort& port = IS_OPENER_PORT_ID(dest_port_id) ?
       iter->second->opener : iter->second->receiver;
 
   DispatchOnMessage(port, message, dest_port_id);
 }
 
 void ExtensionMessageService::DispatchEventToRenderers(
     const std::string& event_name, const std::string& event_args,
     bool has_incognito_data, const GURL& event_url) {
   DCHECK_EQ(MessageLoop::current()->type(), MessageLoop::TYPE_UI);
+  ListenerMap::iterator it = listeners_.find(event_name);
+  if (it == listeners_.end())
+    return;
 
-  std::set<int>& pids = listeners_[event_name];
+  std::set<int>& pids = it->second;
 
   // Send the event only to renderers that are listening for it.
   for (std::set<int>::iterator pid = pids.begin(); pid != pids.end(); ++pid) {
     RenderProcessHost* renderer = RenderProcessHost::FromID(*pid);
     if (!renderer)
       continue;
     if (!ChildProcessSecurityPolicy::GetInstance()->
             HasExtensionBindings(*pid)) {
       // Don't send browser-level events to unprivileged processes.
       continue;
@@ skipping 77 matching lines @@
 
     if (current->second->opener.sender == sender) {
       CloseChannelImpl(current, GET_CHANNEL_OPENER_ID(current->first),
                        notify_other_port);
     } else if (current->second->receiver.sender == sender) {
       CloseChannelImpl(current, GET_CHANNEL_RECEIVERS_ID(current->first),
                        notify_other_port);
     }
   }
 }