Make it clear what last_sync_timestamp actually tracks. Update

chrome/browser/extensions/extension_message_service.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/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 310 matching lines @@
 
 bool ExtensionMessageService::OpenChannelOnUIThreadImpl(
     IPC::Message::Sender* source,
     const std::string& tab_json,
     const MessagePort& receiver, int receiver_port_id,
     const std::string& source_extension_id,
     const std::string& target_extension_id,
     const std::string& channel_name) {
   DCHECK_EQ(MessageLoop::current()->type(), MessageLoop::TYPE_UI);
 
-  // TODO(mpcomplete): notify source if reciever doesn't exist
+  // TODO(mpcomplete): notify source if receiver doesn't exist
   if (!source)
     return false;  // Closed while in flight.
 
   if (!receiver.sender) {
     // Treat it as a disconnect.
     DispatchOnDisconnect(MessagePort(source, MSG_ROUTING_CONTROL),
                          GET_OPPOSITE_PORT_ID(receiver_port_id));
     return false;
   }
 
@@ skipping 200 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);
     }
   }
 }