Add a card background to the app list search result groups.

ui/app_list/views/start_page_view.cc

Index: ui/app_list/views/start_page_view.cc
diff --git a/ui/app_list/views/start_page_view.cc b/ui/app_list/views/start_page_view.cc
index 044a251021185c090656b775fa34b7af1f5982c6..af2f5be8c0a361b8bde9b8c27f9bc7873995834a 100644
--- a/ui/app_list/views/start_page_view.cc
+++ b/ui/app_list/views/start_page_view.cc
@@ -129,6 +129,7 @@ void StartPageView::InitTilesContainer() {
   for (size_t i = 0; i < kNumStartPageTiles; ++i) {
     SearchResultTileItemView* tile_item = new SearchResultTileItemView();
     tiles_container_->AddChildView(tile_item);
+    tile_item->SetTitleBackgroundColor(kLabelBackgroundColor);
     search_result_tile_views_.push_back(tile_item);
   }
 
@@ -137,6 +138,7 @@ void StartPageView::InitTilesContainer() {
       app_list_main_view_->contents_view(),
       view_delegate_->GetModel()->top_level_item_list());
   all_apps_button_->UpdateIcon();
+  all_apps_button_->SetTitleBackgroundColor(kLabelBackgroundColor);
   tiles_container_->AddChildView(all_apps_button_);
 }