Standardize usage of virtual/override/final specifiers.

ui/wm/core/default_activation_client.cc

Index: ui/wm/core/default_activation_client.cc
diff --git a/ui/wm/core/default_activation_client.cc b/ui/wm/core/default_activation_client.cc
index d6383d6d08dc9fed6be69386d0c6a2c57d275fda..20c0d79b7dc7fd121c7d21c236ce38e34581bc1b 100644
--- a/ui/wm/core/default_activation_client.cc
+++ b/ui/wm/core/default_activation_client.cc
@@ -20,10 +20,10 @@ class DefaultActivationClient::Deleter : public aura::WindowObserver {
   }
 
  private:
-  virtual ~Deleter() {}
+  ~Deleter() override {}
 
   // Overridden from WindowObserver:
-  virtual void OnWindowDestroyed(aura::Window* window) override {
+  void OnWindowDestroyed(aura::Window* window) override {
     DCHECK_EQ(window, root_window_);
     root_window_->RemoveObserver(this);
     delete client_;