Add the "virtual" keyword on method overrides that are missing it.

chrome/browser/repost_form_warning_controller.h

Index: chrome/browser/repost_form_warning_controller.h
diff --git a/chrome/browser/repost_form_warning_controller.h b/chrome/browser/repost_form_warning_controller.h
index fb8cf28d941ddd066fc0fbffe83a6c806e0c5c08..e6aef1032ac130e9921c32121ac9474403202ca1 100644
--- a/chrome/browser/repost_form_warning_controller.h
+++ b/chrome/browser/repost_form_warning_controller.h
@@ -32,9 +32,9 @@ class RepostFormWarningController : public NotificationObserver {
  private:
   // NotificationObserver implementation.
   // Watch for a new load or a closed tab and dismiss the dialog if they occur.
-  void Observe(NotificationType type,
-               const NotificationSource& source,
-               const NotificationDetails& details);
+  virtual void Observe(NotificationType type,
+                       const NotificationSource& source,
+                       const NotificationDetails& details);
 
   // Close the warning dialog.
   void CloseDialog();