android: Enable -Wunused-const-variable.

chrome/browser/extensions/api/messaging/message_service.cc

 // Copyright (c) 2012 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/api/messaging/message_service.h"
 
 #include "base/atomic_sequence_num.h"
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/json/json_writer.h"
@@ skipping 42 matching lines @@
 // Port1 is always even, port2 is always odd.
 #define IS_OPENER_PORT_ID(port_id) (((port_id) & 1) == 0)
 
 // Change even to odd and vice versa, to get the other side of a given channel.
 #define GET_OPPOSITE_PORT_ID(source_port_id) ((source_port_id) ^ 1)
 
 namespace extensions {
 
 const char kReceivingEndDoesntExistError[] =
     "Could not establish connection. Receiving end does not exist.";
+#if defined(OS_WIN) || defined(OS_MACOSX) || defined(OS_LINUX)
 const char kMissingPermissionError[] =
     "Access to native messaging requires nativeMessaging permission.";
+#endif
 
 struct MessageService::MessageChannel {
   scoped_ptr<MessagePort> opener;
   scoped_ptr<MessagePort> receiver;
 };
 
 struct MessageService::OpenChannelParams {
   content::RenderProcessHost* source;
   base::DictionaryValue source_tab;
   scoped_ptr<MessagePort> receiver;
@@ skipping 643 matching lines @@
 }
 
 void MessageService::DispatchOnDisconnect(content::RenderProcessHost* source,
                                           int port_id,
                                           const std::string& error_message) {
   ExtensionMessagePort port(source, MSG_ROUTING_CONTROL, "");
   port.DispatchOnDisconnect(GET_OPPOSITE_PORT_ID(port_id), error_message);
 }
 
 }  // namespace extensions