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

BUG=417463
[email protected]

Review URL: https://codereview.chromium.org/648653003

Cr-Commit-Position: refs/heads/master@{#300440}
diff --git a/chrome/browser/browser_keyevents_browsertest.cc b/chrome/browser/browser_keyevents_browsertest.cc
index 49b1ce9..8c95ada3 100644
--- a/chrome/browser/browser_keyevents_browsertest.cc
+++ b/chrome/browser/browser_keyevents_browsertest.cc
@@ -109,9 +109,9 @@
     return finished_;
   }
 
-  virtual void Observe(int type,
-                       const content::NotificationSource& source,
-                       const content::NotificationDetails& details) override {
+  void Observe(int type,
+               const content::NotificationSource& source,
+               const content::NotificationDetails& details) override {
     DCHECK(type == content::NOTIFICATION_DOM_OPERATION_RESPONSE);
     content::Details<DomOperationNotificationDetails> dom_op_details(details);
     // We might receive responses for other script execution, but we only