Remove some UI->FILE->UI thread hops in ExecuteCodeFunction

chrome/browser/chromeos/accessibility/accessibility_manager.cc

 // Copyright (c) 2013 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/chromeos/accessibility/accessibility_manager.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
@@ skipping 167 matching lines @@
   // Finally, call this method once to fetch all of the resources and
   // load them. This method will delete this object when done.
   void Run() {
     if (resources_.empty()) {
       delete this;
       return;
     }
 
     extensions::ExtensionResource resource = resources_.front();
     resources_.pop();
-    scoped_refptr<FileReader> reader(new FileReader(resource, base::Bind(
-        &ContentScriptLoader::OnFileLoaded, base::Unretained(this))));
+    scoped_refptr<FileReader> reader(new FileReader(
+        resource,
+        FileReader::OptionalFileThreadTaskCallback(),  // null callback.
+        base::Bind(&ContentScriptLoader::OnFileLoaded,
+                   base::Unretained(this))));
     reader->Start();
   }
 
  private:
   void OnFileLoaded(bool success, std::unique_ptr<std::string> data) {
     if (success) {
       RenderViewHost* render_view_host =
           RenderViewHost::FromID(render_process_id_, render_view_id_);
       if (render_view_host)
         ExecuteScriptHelper(render_view_host, *data, extension_id_);
@@ skipping 1343 matching lines @@
     content::BrowserContext* context) {
   keyboard_listener_extension_id_ = id;
 
   extensions::ExtensionRegistry* registry =
       extensions::ExtensionRegistry::Get(context);
   if (!extension_registry_observer_.IsObserving(registry) && !id.empty())
     extension_registry_observer_.Add(registry);
 }
 
 }  // namespace chromeos