FolderImage: Const correctness.

ui/app_list/folder_image.h

Index: ui/app_list/folder_image.h
diff --git a/ui/app_list/folder_image.h b/ui/app_list/folder_image.h
index 3006a8666e1960270768063340dae20de66a0bd1..1842d97b41f9725347ab33f5d06b9620b4c8c6f0 100644
--- a/ui/app_list/folder_image.h
+++ b/ui/app_list/folder_image.h
@@ -47,7 +47,7 @@ class APP_LIST_EXPORT FolderImage : public AppListItemListObserver,
   const gfx::ImageSkia& icon() const { return icon_; }
 
   // Returns the icon of one of the top items with |item_index|.
-  const gfx::ImageSkia& GetTopIcon(size_t item_index);
+  const gfx::ImageSkia& GetTopIcon(size_t item_index) const;
 
   // Calculates the top item icons' bounds inside |folder_icon_bounds|.
   // Returns the bounds of top item icons in sequence of top left, top right,
@@ -63,7 +63,7 @@ class APP_LIST_EXPORT FolderImage : public AppListItemListObserver,
   // The Rect returned is in the same coordinates of |folder_icon_bounds|.
   gfx::Rect GetTargetIconRectInFolderForItem(
       AppListItem* item,
-      const gfx::Rect& folder_icon_bounds);
+      const gfx::Rect& folder_icon_bounds) const;
 
   void AddObserver(FolderImageObserver* observer);
   void RemoveObserver(FolderImageObserver* observer);