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

chrome/browser/extensions/api/system_storage/system_storage_apitest.cc

Index: chrome/browser/extensions/api/system_storage/system_storage_apitest.cc
diff --git a/chrome/browser/extensions/api/system_storage/system_storage_apitest.cc b/chrome/browser/extensions/api/system_storage/system_storage_apitest.cc
index f5a4985a9bc808d6bde9809e9a1328f230f78e79..c5353741ecec9df54470d69e231a38459dc54a0e 100644
--- a/chrome/browser/extensions/api/system_storage/system_storage_apitest.cc
+++ b/chrome/browser/extensions/api/system_storage/system_storage_apitest.cc
@@ -36,10 +36,10 @@ class TestStorageInfoProvider : public extensions::StorageInfoProvider {
                           size_t n);
 
  private:
-  virtual ~TestStorageInfoProvider();
+  ~TestStorageInfoProvider() override;
 
   // StorageInfoProvider implementations.
-  virtual double GetStorageFreeSpaceFromTransientIdOnFileThread(
+  double GetStorageFreeSpaceFromTransientIdOnFileThread(
       const std::string& transient_id) override;
 
   std::vector<struct TestStorageUnitInfo> testing_data_;
@@ -71,11 +71,11 @@ class SystemStorageApiTest : public ExtensionApiTest {
   SystemStorageApiTest() {}
   virtual ~SystemStorageApiTest() {}
 
-  virtual void SetUpOnMainThread() override {
+  void SetUpOnMainThread() override {
     TestStorageMonitor::CreateForBrowserTests();
   }
 
-  virtual void SetUpInProcessBrowserTestFixture() override {
+  void SetUpInProcessBrowserTestFixture() override {
     ExtensionApiTest::SetUpInProcessBrowserTestFixture();
     message_loop_.reset(new base::MessageLoopForUI);
   }