Standardize usage of virtual/override/final specifiers.

extensions/shell/browser/shell_display_info_provider.h

Index: extensions/shell/browser/shell_display_info_provider.h
diff --git a/extensions/shell/browser/shell_display_info_provider.h b/extensions/shell/browser/shell_display_info_provider.h
index a68bcd50a9f3c174cb4d84a9a0fe18a408b8a621..61cea1cc7f2ed5c882a3022a2fcd3943dce62021 100644
--- a/extensions/shell/browser/shell_display_info_provider.h
+++ b/extensions/shell/browser/shell_display_info_provider.h
@@ -12,16 +12,16 @@ namespace extensions {
 class ShellDisplayInfoProvider : public DisplayInfoProvider {
  public:
   ShellDisplayInfoProvider();
-  virtual ~ShellDisplayInfoProvider();
+  ~ShellDisplayInfoProvider() override;
 
   // DisplayInfoProvider implementation.
-  virtual bool SetInfo(const std::string& display_id,
-                       const core_api::system_display::DisplayProperties& info,
-                       std::string* error) override;
-  virtual void UpdateDisplayUnitInfoForPlatform(
+  bool SetInfo(const std::string& display_id,
+               const core_api::system_display::DisplayProperties& info,
+               std::string* error) override;
+  void UpdateDisplayUnitInfoForPlatform(
       const gfx::Display& display,
       extensions::core_api::system_display::DisplayUnitInfo* unit) override;
-  virtual gfx::Screen* GetActiveScreen() override;
+  gfx::Screen* GetActiveScreen() override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ShellDisplayInfoProvider);