Experimental app list: "All apps" button has a folder-like icon.

ui/app_list/folder_image.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_FOLDER_IMAGE_H_
+#define UI_APP_LIST_FOLDER_IMAGE_H_
+
+#include <vector>
+
+#include "base/observer_list.h"
+#include "ui/app_list/app_list_item_list_observer.h"
+#include "ui/app_list/app_list_item_observer.h"
+
+namespace gfx {
+class ImageSkia;
+class Rect;
+}
+
+namespace app_list {
+
+class AppListItem;
+class AppListItemList;
+
+class FolderImageObserver {
+ public:
+  // Called when the folder icon has changed.
+  virtual void OnFolderImageUpdated(const gfx::ImageSkia& icon) {}

[calamity, 2014/10/28 05:12:58]

I think it would be less weird to have this with no params and then let the
observer read the icon out of this class.

[Matt Giuca, 2014/10/29 07:11:23]

Done.

+
+ protected:
+  virtual ~FolderImageObserver() {}
+};
+
+// The icon for an app list folder, dynamically generated by drawing the
+// folder's items inside a circle. Automatically keeps itself up to date.
+// Does not directly store the icon; just passes it for the observers to use.

[calamity, 2014/10/28 05:12:57]

Any reason not to store the icon? It would make this class more standaloney and
testable.

In fact, this class could use with a test.

[Matt Giuca, 2014/10/29 07:11:23]

Done.
Done.

+class FolderImage : public AppListItemListObserver, public AppListItemObserver {
+ public:
+  FolderImage(AppListItemList* item_list);
+

[calamity, 2014/10/28 05:12:57]

nit: no space

[Matt Giuca, 2014/10/29 07:11:23]

Done.

+  ~FolderImage() override;
+
+  // Generates the folder's icon from the icons of the items in the item list,
+  // and calls OnFolderImageUpdated with the result.
+  void UpdateIcon();
+
+  // Returns the icon of one of the top items with |item_index|.
+  const gfx::ImageSkia& GetTopIcon(size_t item_index);
+
+  // Returns the target icon bounds for |item| to fly back to its parent folder
+  // icon in animation UI. If |item| is one of the top item icon, this will
+  // match its corresponding top item icon in the folder icon. Otherwise,
+  // the target icon bounds is centered at the |folder_icon_bounds| with
+  // the same size of the top item icon.
+  // The Rect returned is in the same coordinates of |folder_icon_bounds|.
+  gfx::Rect GetTargetIconRectInFolderForItem(
+      AppListItem* item,
+      const gfx::Rect& folder_icon_bounds);
+
+  void AddObserver(FolderImageObserver* observer);
+  void RemoveObserver(FolderImageObserver* observer);
+
+  // AppListItemObserver overrides:

[calamity, 2014/10/28 05:12:58]

Overridden from

[Matt Giuca, 2014/10/29 07:11:23]

Nah.

+  void ItemIconChanged() override;
+
+  // AppListItemListObserver overrides:

[calamity, 2014/10/28 05:12:58]

Overridden from

+  void OnListItemAdded(size_t index, AppListItem* item) override;
+  void OnListItemRemoved(size_t index, AppListItem* item) override;
+  void OnListItemMoved(size_t from_index,
+                       size_t to_index,
+                       AppListItem* item) override;
+
+ private:
+  // Updates the folder's icon from the icons of |top_items_| and calls
+  // OnFolderImageUpdated. Does not refresh the |top_items_| list, so should
+  // only be called if the |item_list_| has not been changed (see UpdateIcon).
+  void UpdateImageOnly();
+
+  // List of top-level app list items (to display small in the icon).
+  AppListItemList* item_list_;
+
+  // Top items for generating folder icon.
+  std::vector<AppListItem*> top_items_;
+
+  ObserverList<FolderImageObserver> observers_;
+};
+
+}  // namespace app_list
+
+#endif  // UI_APP_LIST_FOLDER_IMAGE_H_