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

chrome/browser/history/delete_directive_handler.cc

Index: chrome/browser/history/delete_directive_handler.cc
diff --git a/chrome/browser/history/delete_directive_handler.cc b/chrome/browser/history/delete_directive_handler.cc
index 1a42b88a89f97c7ecbb2df1ad31c5ab3d09eb431..405cc7dbf9c976163a9595b8748095e150b1e51e 100644
--- a/chrome/browser/history/delete_directive_handler.cc
+++ b/chrome/browser/history/delete_directive_handler.cc
@@ -124,12 +124,12 @@ class DeleteDirectiveHandler::DeleteDirectiveTask : public HistoryDBTask {
        post_processing_action_(post_processing_action) {}
 
   // Implements HistoryDBTask.
-  virtual bool RunOnDBThread(history::HistoryBackend* backend,
-                             history::HistoryDatabase* db) override;
-  virtual void DoneRunOnMainThread() override;
+  bool RunOnDBThread(history::HistoryBackend* backend,
+                     history::HistoryDatabase* db) override;
+  void DoneRunOnMainThread() override;
 
  private:
-  virtual ~DeleteDirectiveTask() {}
+  ~DeleteDirectiveTask() override {}
 
   // Process a list of global Id directives. Delete all visits to a URL in
   // time ranges of directives if the timestamp of one visit matches with one