Refactor app list event handling and prerendering.

ui/app_list/views/apps_grid_view.cc

Index: ui/app_list/views/apps_grid_view.cc
diff --git a/ui/app_list/views/apps_grid_view.cc b/ui/app_list/views/apps_grid_view.cc
index f150eb6b6802d80162520ddfe390c0bbcac19581..d28be107a3bec46b8b90fec6c7c373cf82d4f4da 100644
--- a/ui/app_list/views/apps_grid_view.cc
+++ b/ui/app_list/views/apps_grid_view.cc
@@ -846,11 +846,12 @@ void AppsGridView::SetDragAndDropHostOfCurrentAppList(
   drag_and_drop_host_ = drag_and_drop_host;
 }
 
-void AppsGridView::Prerender(int page_index) {
+void AppsGridView::Prerender() {
   Layout();
-  int start = std::max(0, (page_index - kPrerenderPages) * tiles_per_page());
+  int selected_page = std::max(0, pagination_model_.selected_page());
+  int start = std::max(0, (selected_page - kPrerenderPages) * tiles_per_page());
   int end = std::min(view_model_.view_size(),
-                     (page_index + 1 + kPrerenderPages) * tiles_per_page());
+                     (selected_page + 1 + kPrerenderPages) * tiles_per_page());
   for (int i = start; i < end; i++) {
     AppListItemView* v = static_cast<AppListItemView*>(view_model_.view_at(i));
     v->Prerender();