Store AppItems as pages in AppListModel.

ui/app_list/views/app_list_main_view.cc

Index: ui/app_list/views/app_list_main_view.cc
diff --git a/ui/app_list/views/app_list_main_view.cc b/ui/app_list/views/app_list_main_view.cc
index 792c5bd8355bdfa59d059de8d239026b526b92cb..10faa0a3fa0ef2dcb3f86f81685833d560cb1508 100644
--- a/ui/app_list/views/app_list_main_view.cc
+++ b/ui/app_list/views/app_list_main_view.cc
@@ -148,6 +148,9 @@ void AppListMainView::SetDragAndDropHostOfCurrentAppList(
 
 void AppListMainView::PreloadIcons(PaginationModel* pagination_model,
                                    gfx::NativeView parent) {
+  if (model_->GetNumAppPages() == 0)
+    return;
+
   ui::ScaleFactor scale_factor = ui::SCALE_FACTOR_100P;
   if (parent)
     scale_factor = ui::GetScaleFactorForNativeView(parent);
@@ -155,17 +158,16 @@ void AppListMainView::PreloadIcons(PaginationModel* pagination_model,
   float scale = ui::GetImageScale(scale_factor);
   // |pagination_model| could have -1 as the initial selected page and
   // assumes first page (i.e. index 0) will be used in this case.
-  const int selected_page = std::max(0, pagination_model->selected_page());
-
-  const int tiles_per_page = kPreferredCols * kPreferredRows;
-  const int start_model_index = selected_page * tiles_per_page;
-  const int end_model_index = std::min(
-      static_cast<int>(model_->apps()->item_count()),
-      start_model_index + tiles_per_page);
-
+  size_t selected_page = 0;
+  if (pagination_model->selected_page() > 0) {
+    selected_page = static_cast<size_t>(pagination_model->selected_page());
+    selected_page = std::min(selected_page, model_->GetNumAppPages() - 1);
+  }
   pending_icon_loaders_.clear();
-  for (int i = start_model_index; i < end_model_index; ++i) {
-    AppListItemModel* item = model_->apps()->GetItemAt(i);
+  const AppListModel::AppItems& apps =
+      model_->GetAppItemsForPage(selected_page);
+  for (size_t i = 0; i < apps.item_count(); ++i) {
+    AppListItemModel* item = model_->GetItemAt(selected_page, i);
     if (item->icon().HasRepresentation(scale))
       continue;