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

chrome/browser/browsing_data_remover.h

Index: chrome/browser/browsing_data_remover.h
diff --git a/chrome/browser/browsing_data_remover.h b/chrome/browser/browsing_data_remover.h
index a1601983d52780c997472021c4ce32bd388d2299..8249e6ba5368195ea9ecdd7440272526507a6905 100644
--- a/chrome/browser/browsing_data_remover.h
+++ b/chrome/browser/browsing_data_remover.h
@@ -97,9 +97,9 @@ class BrowsingDataRemover : public NotificationObserver {
   // NotificationObserver method. Callback when TemplateURLModel has finished
   // loading. Deletes the entries from the model, and if we're not waiting on
   // anything else notifies observers and deletes this BrowsingDataRemover.
-  void Observe(NotificationType type,
-               const NotificationSource& source,
-               const NotificationDetails& details);
+  virtual void Observe(NotificationType type,
+                       const NotificationSource& source,
+                       const NotificationDetails& details);
 
   // If we're not waiting on anything, notifies observers and deletes this
   // object.