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

chrome/browser/chromeos/accessibility/accessibility_extension_loader.cc

Index: chrome/browser/chromeos/accessibility/accessibility_extension_loader.cc
diff --git a/chrome/browser/chromeos/accessibility/accessibility_extension_loader.cc b/chrome/browser/chromeos/accessibility/accessibility_extension_loader.cc
index 9360b98fb367f3d5d0d96dc5ddab4e46ec48676c..34faf17da30607ab12b4f4bf9485125eb4f28c98 100644
--- a/chrome/browser/chromeos/accessibility/accessibility_extension_loader.cc
+++ b/chrome/browser/chromeos/accessibility/accessibility_extension_loader.cc
@@ -90,9 +90,11 @@ class ContentScriptLoader {
 
     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();
   }