patch from issue 2577273002 at patchset 20001 (http://crrev.com/2577273002#ps20001)

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 b2db32545cc1721a00cafc7d9c4e35cf62092785..4276d75987744ea9b1902fcdc303f976eac2410c 100644
--- a/chrome/browser/icon_loader.h
+++ b/chrome/browser/icon_loader.h
@@ -8,9 +8,9 @@
 #include <memory>
 #include <string>
 
+#include "base/callback.h"
 #include "base/files/file_path.h"
 #include "base/macros.h"
-#include "base/memory/ref_counted.h"
 #include "base/single_thread_task_runner.h"
 #include "build/build_config.h"
 #include "content/public/browser/browser_thread.h"
@@ -22,7 +22,7 @@
 // thread. Returns the icon in the form of an ImageSkia.
 //
 ////////////////////////////////////////////////////////////////////////////////
-class IconLoader : public base::RefCountedThreadSafe<IconLoader> {
+class IconLoader {
  public:
   // An IconGroup is a class of files that all share the same icon. For all
   // platforms but Windows, and for most files on Windows, it is the file type
@@ -39,31 +39,22 @@ class IconLoader : public base::RefCountedThreadSafe<IconLoader> {
     ALL,        // All sizes available
   };
 
-  class Delegate {
-   public:
-    // Invoked when an icon has been read. |source| is the IconLoader. If the
-    // icon has been successfully loaded, |result| is non-null. |group| is the
-    // determined group from the original requested path.
-    virtual void OnImageLoaded(IconLoader* source,
-                               std::unique_ptr<gfx::Image> result,
-                               const IconGroup& group) = 0;
-
-   protected:
-    virtual ~Delegate() {}
-  };
+  // The callback invoked when an icon has been read. The parameters are:
+  // - The IconLoader.
+  // - The icon that was loaded, or null if there was a failure to load it.
+  // - The determined group from the original requested path.
+  using IconLoadedCallback = base::OnceCallback<
+      void(IconLoader*, std::unique_ptr<gfx::Image>, const IconGroup&)>;
 
   IconLoader(const base::FilePath& file_path,
              IconSize size,
-             Delegate* delegate);
+             IconLoadedCallback callback);
+  ~IconLoader();
 
   // Start reading the icon on the file thread.
   void Start();
 
  private:
-  friend class base::RefCountedThreadSafe<IconLoader>;
-
-  virtual ~IconLoader();
-
   // Given a file path, get the group for the given file.
   static IconGroup GroupForFilepath(const base::FilePath& file_path);
 
@@ -74,8 +65,6 @@ class IconLoader : public base::RefCountedThreadSafe<IconLoader> {
   void OnReadGroup();
   void ReadIcon();
 
-  void NotifyDelegate();
-
   // The task runner object of the thread in which we notify the delegate.
   scoped_refptr<base::SingleThreadTaskRunner> target_task_runner_;
 
@@ -87,7 +76,7 @@ class IconLoader : public base::RefCountedThreadSafe<IconLoader> {
 
   std::unique_ptr<gfx::Image> image_;
 
-  Delegate* delegate_;
+  IconLoadedCallback callback_;
 
   DISALLOW_COPY_AND_ASSIGN(IconLoader);
 };