Standardize usage of virtual/override/final specifiers.

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 7ed229c53a441bc3fe7c4bd049170a370c94676b..04585c368782a27e6c39869a996ae77b436ec703 100644
--- a/ui/app_list/views/app_list_main_view.cc
+++ b/ui/app_list/views/app_list_main_view.cc
@@ -57,13 +57,11 @@ class AppListMainView::IconLoader : public AppListItemObserver {
     item_->icon().GetRepresentation(scale);
   }
 
-  virtual ~IconLoader() {
-    item_->RemoveObserver(this);
-  }
+  ~IconLoader() override { item_->RemoveObserver(this); }
 
  private:
   // AppListItemObserver overrides:
-  virtual void ItemIconChanged() override {
+  void ItemIconChanged() override {
     owner_->OnItemIconLoaded(this);
     // Note that IconLoader is released here.
   }