Make apps grid view scroll vertically in experimental app list.

ui/app_list/views/apps_grid_view.h

Index: ui/app_list/views/apps_grid_view.h
diff --git a/ui/app_list/views/apps_grid_view.h b/ui/app_list/views/apps_grid_view.h
index 0e470a28bd125a96fb7eb1882d1e8d9b0243c2fa..546d1f8bc812a88ab14c2f09f69f8a86446ff7d1 100644
--- a/ui/app_list/views/apps_grid_view.h
+++ b/ui/app_list/views/apps_grid_view.h
@@ -224,6 +224,8 @@ class APP_LIST_EXPORT AppsGridView : public views::View,
     DROP_FOR_FOLDER,
   };
 
+  enum ScrollAxis { SCROLL_AXIS_HORIZONTAL, SCROLL_AXIS_VERTICAL };
+
   // Represents the index to an item view in the grid.
   struct Index {
     Index() : page(-1), slot(-1) {}
@@ -459,6 +461,9 @@ class APP_LIST_EXPORT AppsGridView : public views::View,
                          const base::FilePath& path);
 #endif
 
+  // Determines whether the grid view scrolls horizontally or vertically.
+  static ScrollAxis GetScrollAxis();
+
   AppListModel* model_;  // Owned by AppListView.
   AppListItemList* item_list_;  // Not owned.
   AppsGridViewDelegate* delegate_;