Standardize usage of virtual/override/final specifiers.

ash/shell/content_client/shell_main_delegate.h

Index: ash/shell/content_client/shell_main_delegate.h
diff --git a/ash/shell/content_client/shell_main_delegate.h b/ash/shell/content_client/shell_main_delegate.h
index b506a1bf0bd8265ab520f8e18905eec5e024b3c5..7daf1fa4405f456c4c0def0ee743fcfb9fc313ce 100644
--- a/ash/shell/content_client/shell_main_delegate.h
+++ b/ash/shell/content_client/shell_main_delegate.h
@@ -24,11 +24,11 @@ class ShellContentBrowserClient;
 class ShellMainDelegate : public content::ContentMainDelegate {
  public:
   ShellMainDelegate();
-  virtual ~ShellMainDelegate();
+  ~ShellMainDelegate() override;
 
-  virtual bool BasicStartupComplete(int* exit_code) override;
-  virtual void PreSandboxStartup() override;
-  virtual content::ContentBrowserClient* CreateContentBrowserClient() override;
+  bool BasicStartupComplete(int* exit_code) override;
+  void PreSandboxStartup() override;
+  content::ContentBrowserClient* CreateContentBrowserClient() override;
 
  private:
   void InitializeResourceBundle();