Standardize usage of virtual/override/final in chrome/browser/extensions/

chrome/browser/extensions/install_signer.cc

Index: chrome/browser/extensions/install_signer.cc
diff --git a/chrome/browser/extensions/install_signer.cc b/chrome/browser/extensions/install_signer.cc
index 74dc76b5db6f444893cad25b4d8358136dfcbbc8..8d4c35eb4d1b9816267ded36e0b843d4752a18a3 100644
--- a/chrome/browser/extensions/install_signer.cc
+++ b/chrome/browser/extensions/install_signer.cc
@@ -274,10 +274,9 @@ class InstallSigner::FetcherDelegate : public net::URLFetcherDelegate {
       : callback_(callback) {
   }
 
-  virtual ~FetcherDelegate() {
-  }
+  ~FetcherDelegate() override {}
 
-  virtual void OnURLFetchComplete(const net::URLFetcher* source) override {
+  void OnURLFetchComplete(const net::URLFetcher* source) override {
     callback_.Run();
   }