Moved FolderImageSource class to a separate file.

ui/app_list/app_list_folder_item.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_APP_LIST_APP_LIST_FOLDER_ITEM_H_
 #define UI_APP_LIST_APP_LIST_FOLDER_ITEM_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 50 matching lines @@
 
   // AppListItem
   void Activate(int event_flags) override;
   const char* GetItemType() const override;
   ui::MenuModel* GetContextMenuModel() override;
   AppListItem* FindChildItem(const std::string& id) override;
   size_t ChildItemCount() const override;
   void OnExtensionPreferenceChanged() override;
   bool CompareForTest(const AppListItem* other) const override;
 
-  // Calculates the top item icons' bounds inside |folder_icon_bounds|.
-  // Returns the bounds of top item icons in sequence of top left, top right,
-  // bottom left, bottom right.
-  static std::vector<gfx::Rect> GetTopIconsBounds(
-      const gfx::Rect& folder_icon_bounds);
-
   // Returns an id for a new folder.
   static std::string GenerateId();
 
  private:
   // AppListItemObserver
   void ItemIconChanged() override;
 
   // AppListItemListObserver
   void OnListItemAdded(size_t index, AppListItem* item) override;
   void OnListItemRemoved(size_t index, AppListItem* item) override;
@@ skipping 12 matching lines @@
 
   // Top items for generating folder icon.
   std::vector<AppListItem*> top_items_;
 
   DISALLOW_COPY_AND_ASSIGN(AppListFolderItem);
 };
 
 }  // namespace app_list
 
 #endif  // UI_APP_LIST_APP_LIST_FOLDER_ITEM_H_