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

ui/app_list/views/all_apps_tile_item_view.h

Index: ui/app_list/views/all_apps_tile_item_view.h
diff --git a/ui/app_list/views/all_apps_tile_item_view.h b/ui/app_list/views/all_apps_tile_item_view.h
index da3a3ad60736087fbcd4c2a8a39c86ac3468aac5..150d5535af49c1206ab47c96b36b71947326b38b 100644
--- a/ui/app_list/views/all_apps_tile_item_view.h
+++ b/ui/app_list/views/all_apps_tile_item_view.h
@@ -7,24 +7,34 @@
 
 #include <vector>
 
+#include "ui/app_list/folder_image.h"
 #include "ui/app_list/views/tile_item_view.h"
 
 namespace app_list {
 
+class AppListItemList;
 class ContentsView;
 
 // A tile item for the "All apps" button on the start page.
-class AllAppsTileItemView : public TileItemView {
+class AllAppsTileItemView : public TileItemView, public FolderImageObserver {
  public:
-  AllAppsTileItemView(ContentsView* contents_view);
+  AllAppsTileItemView(ContentsView* contents_view, AppListItemList* item_list);
 
   ~AllAppsTileItemView() override;
 
+  // Generates the folder's icon from the icons of the items in the item list.
+  void UpdateIcon();
+
   // TileItemView overrides:
   void ButtonPressed(views::Button* sender, const ui::Event& event) override;
 
+  // FolderImageObserver overrides:
+  void OnFolderImageUpdated() override;
+
  private:
   ContentsView* contents_view_;
+
+  FolderImage folder_image_;
 };
 
 }  // namespace app_list