Standardize usage of virtual/override/final specifiers.

ash/shell/content_client/shell_browser_main_parts.cc

Index: ash/shell/content_client/shell_browser_main_parts.cc
diff --git a/ash/shell/content_client/shell_browser_main_parts.cc b/ash/shell/content_client/shell_browser_main_parts.cc
index c41c0301d7093ee23edbefedb3d5e6448e7ee895..e0d55c2d97520c6be2fd51fe5d4708a04054fd57 100644
--- a/ash/shell/content_client/shell_browser_main_parts.cc
+++ b/ash/shell/content_client/shell_browser_main_parts.cc
@@ -51,14 +51,14 @@ namespace {
 class ShellViewsDelegate : public views::TestViewsDelegate {
  public:
   ShellViewsDelegate() {}
-  virtual ~ShellViewsDelegate() {}
+  ~ShellViewsDelegate() override {}
 
   // Overridden from views::TestViewsDelegate:
-  virtual views::NonClientFrameView* CreateDefaultNonClientFrameView(
+  views::NonClientFrameView* CreateDefaultNonClientFrameView(
       views::Widget* widget) override {
     return ash::Shell::GetInstance()->CreateDefaultNonClientFrameView(widget);
   }
-  virtual void OnBeforeWidgetInit(
+  void OnBeforeWidgetInit(
       views::Widget::InitParams* params,
       views::internal::NativeWidgetDelegate* delegate) override {
     if (params->opacity == views::Widget::InitParams::INFER_OPACITY)