Switch IconLoader::ReadIconThreadID from FILE to UI

chrome/browser/icon_loader_chromeos.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/icon_loader.h"
 
 #include <stddef.h>
 
 #include <map>
 #include <string>
@@ skipping 174 matching lines @@
 }  // namespace
 
 // static
 IconLoader::IconGroup IconLoader::GroupForFilepath(
     const base::FilePath& file_path) {
   return base::ToLowerASCII(file_path.Extension());
 }
 
 // static
 content::BrowserThread::ID IconLoader::ReadIconThreadID() {
-  return content::BrowserThread::FILE;
+  return content::BrowserThread::UI;

[sky, 2017/02/22 17:12:02]

Please add a comment. It isn't readily obvious why it's ok to do the processing
on the ui thread.

[tzik, 2017/02/22 22:02:56]

Done.

 }
 
 void IconLoader::ReadIcon() {
   static base::LazyInstance<IconMapper>::Leaky icon_mapper =
       LAZY_INSTANCE_INITIALIZER;
   int idr = icon_mapper.Get().Lookup(group_, icon_size_);
   ResourceBundle& rb = ResourceBundle::GetSharedInstance();
   gfx::ImageSkia image_skia(ResizeImage(*(rb.GetImageNamed(idr)).ToImageSkia(),
                                         IconSizeToDIPSize(icon_size_)));
   image_skia.MakeThreadSafe();
   std::unique_ptr<gfx::Image> image = base::MakeUnique<gfx::Image>(image_skia);
   target_task_runner_->PostTask(
       FROM_HERE, base::Bind(callback_, base::Passed(&image), group_));
   delete this;
 }