Switch IconLoader::ReadIconThreadID from FILE to UI

chrome/browser/icon_loader_chromeos.cc

Index: chrome/browser/icon_loader_chromeos.cc
diff --git a/chrome/browser/icon_loader_chromeos.cc b/chrome/browser/icon_loader_chromeos.cc
index 52ae44d7b2d49be7f0d268e3dbec62355062d325..a68d8c49300b037fbaa9c8a83ea5f99e49a340f0 100644
--- a/chrome/browser/icon_loader_chromeos.cc
+++ b/chrome/browser/icon_loader_chromeos.cc
@@ -192,7 +192,7 @@ IconLoader::IconGroup IconLoader::GroupForFilepath(
 
 // 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() {