Moved FolderImageSource class to a separate file.

ui/app_list/folder_image_source.h

+// Copyright 2014 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_IMAGE_SOURCE_H_
+#define UI_APP_LIST_APP_LIST_FOLDER_IMAGE_SOURCE_H_
+
+#include <vector>
+
+#include "ui/gfx/image/canvas_image_source.h"
+
+namespace gfx {
+class Canvas;
+class ImageSkia;
+class Rect;
+class Size;
+}
+
+namespace app_list {
+
+// Generates the folder icon with the top 4 child item icons laid in 2x2 tile.
+class FolderImageSource : public gfx::CanvasImageSource {
+ public:
+  typedef std::vector<gfx::ImageSkia> Icons;
+
+  FolderImageSource(const Icons& icons, const gfx::Size& size);
+  ~FolderImageSource() override;
+
+  // Gets the size of a small app icon inside the folder icon.
+  static gfx::Size ItemIconSize();
+
+  // 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);
+
+ private:
+  void DrawIcon(gfx::Canvas* canvas,
+                const gfx::ImageSkia& icon,
+                const gfx::Size icon_size,
+                int x,
+                int y);
+
+  // gfx::CanvasImageSource overrides:
+  void Draw(gfx::Canvas* canvas) override;
+
+  Icons icons_;
+  gfx::Size size_;
+
+  DISALLOW_COPY_AND_ASSIGN(FolderImageSource);
+};
+
+}  // namespace app_list
+
+#endif  // UI_APP_LIST_APP_LIST_FOLDER_ITEM_H_