extensions: Speculative fix for crash on IO thread.

extensions/browser/extension_function_dispatcher.cc

 // Copyright 2014 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 "extensions/browser/extension_function_dispatcher.h"
 
 #include "base/bind.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
@@ skipping 213 matching lines @@
 // static
 void ExtensionFunctionDispatcher::DispatchOnIOThread(
     InfoMap* extension_info_map,
     void* profile_id,
     int render_process_id,
     base::WeakPtr<ExtensionMessageFilter> ipc_sender,
     int routing_id,
     const ExtensionHostMsg_Request_Params& params) {
   const Extension* extension =
       extension_info_map->extensions().GetByID(params.extension_id);
+  if (!extension)
+    return;
 
   ExtensionFunction::ResponseCallback callback(
       base::Bind(&IOThreadResponseCallback, ipc_sender, routing_id,
                  params.request_id));
 
   scoped_refptr<ExtensionFunction> function(
       CreateExtensionFunction(params,
                               extension,
                               render_process_id,
                               extension_info_map->process_map(),
@@ skipping 218 matching lines @@
 
 // static
 void ExtensionFunctionDispatcher::SendAccessDenied(
     const ExtensionFunction::ResponseCallback& callback) {
   base::ListValue empty_list;
   callback.Run(ExtensionFunction::FAILED, empty_list,
                "Access to extension API denied.");
 }
 
 }  // namespace extensions