Update {virtual,override,final} to follow C++11 style in ash.

ash/display/display_manager.h

Index: ash/display/display_manager.h
diff --git a/ash/display/display_manager.h b/ash/display/display_manager.h
index d9e4efa27c78427b23d04e1228092cbc5d6c6aef..092d2b002961288a666af8254c5029df6edf93e5 100644
--- a/ash/display/display_manager.h
+++ b/ash/display/display_manager.h
@@ -78,7 +78,11 @@ class ASH_EXPORT DisplayManager
   };
 
   DisplayManager();
+#if defined(OS_CHROMEOS)
+  ~DisplayManager() override;
+#else
   virtual ~DisplayManager();
+#endif
 
   DisplayLayoutStore* layout_store() {
     return layout_store_.get();
@@ -270,8 +274,8 @@ class ASH_EXPORT DisplayManager
 
   // SoftwareMirroringController override:
 #if defined(OS_CHROMEOS)
-  virtual void SetSoftwareMirroring(bool enabled) override;
-  virtual bool SoftwareMirroringEnabled() const override;
+  void SetSoftwareMirroring(bool enabled) override;
+  bool SoftwareMirroringEnabled() const override;
 #endif
   bool software_mirroring_enabled() const {
     return second_display_mode_ == MIRRORING;