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..30f0005b8a7d2922c2b83145ecc951ffc76089d1 100644
--- a/chrome/browser/icon_loader_chromeos.cc
+++ b/chrome/browser/icon_loader_chromeos.cc
@@ -192,7 +192,9 @@ IconLoader::IconGroup IconLoader::GroupForFilepath(
 
 // static
 content::BrowserThread::ID IconLoader::ReadIconThreadID() {
-  return content::BrowserThread::FILE;
+  // ReadIcon touches non thread safe ResourceBundle images, so it must be on
+  // the UI thread.
+  return content::BrowserThread::UI;
 }
 
 void IconLoader::ReadIcon() {