Move the IconLoader to use the task scheduler.

chrome/browser/icon_loader_mac.mm

Index: chrome/browser/icon_loader_mac.mm
diff --git a/chrome/browser/icon_loader_mac.mm b/chrome/browser/icon_loader_mac.mm
index 392f2b22b2535953baf0b4b6b1f66e169aec7f91..123a7f2792dd450b744ada9f178b2b075db10522 100644
--- a/chrome/browser/icon_loader_mac.mm
+++ b/chrome/browser/icon_loader_mac.mm
@@ -11,6 +11,7 @@
 #include "base/memory/ptr_util.h"
 #include "base/message_loop/message_loop.h"
 #include "base/strings/sys_string_conversions.h"
+#include "base/task_scheduler/post_task.h"
 #include "base/threading/thread.h"
 #include "ui/gfx/image/image_skia.h"
 #include "ui/gfx/image/image_skia_util_mac.h"
@@ -22,8 +23,9 @@ IconLoader::IconGroup IconLoader::GroupForFilepath(
 }
 
 // static
-content::BrowserThread::ID IconLoader::ReadIconThreadID() {
-  return content::BrowserThread::FILE;
+scoped_refptr<base::TaskRunner> IconLoader::ReadIconTaskRunner() {
+  // NSWorkspace is thread-safe.
+  return base::CreateTaskRunnerWithTraits(traits());
 }
 
 void IconLoader::ReadIcon() {