Standardize usage of virtual/override/final in extensions/

extensions/common/manifest_handlers/background_info.h

Index: extensions/common/manifest_handlers/background_info.h
diff --git a/extensions/common/manifest_handlers/background_info.h b/extensions/common/manifest_handlers/background_info.h
index cc96a1adc7da5db1b83dfc012023789cecf1b12d..87c2f1218d5f7918a5fe5e179649e78c43448734 100644
--- a/extensions/common/manifest_handlers/background_info.h
+++ b/extensions/common/manifest_handlers/background_info.h
@@ -18,7 +18,7 @@ namespace extensions {
 class BackgroundInfo : public Extension::ManifestData {
  public:
   BackgroundInfo();
-  virtual ~BackgroundInfo();
+  ~BackgroundInfo() override;
 
   static GURL GetBackgroundURL(const Extension* extension);
   static const std::vector<std::string>& GetBackgroundScripts(
@@ -81,16 +81,16 @@ class BackgroundInfo : public Extension::ManifestData {
 class BackgroundManifestHandler : public ManifestHandler {
  public:
   BackgroundManifestHandler();
-  virtual ~BackgroundManifestHandler();
+  ~BackgroundManifestHandler() override;
 
-  virtual bool Parse(Extension* extension, base::string16* error) override;
-  virtual bool Validate(const Extension* extension,
-                        std::string* error,
-                        std::vector<InstallWarning>* warnings) const override;
-  virtual bool AlwaysParseForType(Manifest::Type type) const override;
+  bool Parse(Extension* extension, base::string16* error) override;
+  bool Validate(const Extension* extension,
+                std::string* error,
+                std::vector<InstallWarning>* warnings) const override;
+  bool AlwaysParseForType(Manifest::Type type) const override;
 
  private:
-  virtual const std::vector<std::string> Keys() const override;
+  const std::vector<std::string> Keys() const override;
 
   DISALLOW_COPY_AND_ASSIGN(BackgroundManifestHandler);
 };