Move the IconLoader to use the task scheduler.

chrome/browser/icon_loader.h

Index: chrome/browser/icon_loader.h
diff --git a/chrome/browser/icon_loader.h b/chrome/browser/icon_loader.h
index 837be967356c45ed26169a6b9091a2185073bee2..29a22fcfaa94d19a6a675f74e813c73d3c5ea9ef 100644
--- a/chrome/browser/icon_loader.h
+++ b/chrome/browser/icon_loader.h
@@ -66,8 +66,8 @@ class IconLoader {
   // Given a file path, get the group for the given file.
   static IconGroup GroupForFilepath(const base::FilePath& file_path);
 
-  // The thread ReadIcon() should be called on.
-  static content::BrowserThread::ID ReadIconThreadID();
+  // Whether ReadIcon() must be called on the UI thread.
+  static bool ReadIconRequiresUIThread();
 
   void ReadGroup();
   void OnReadGroup();