Add a virtual destructor to WebNotificationDelegate.

public/platform/modules/notifications/WebNotificationDelegate.h

Index: public/platform/modules/notifications/WebNotificationDelegate.h
diff --git a/public/platform/modules/notifications/WebNotificationDelegate.h b/public/platform/modules/notifications/WebNotificationDelegate.h
index 5c77233e2320a4fbea7d8a069d44734d8900ceed..f13731410cdd798b92609aa3ea04cf4ca570f4b6 100644
--- a/public/platform/modules/notifications/WebNotificationDelegate.h
+++ b/public/platform/modules/notifications/WebNotificationDelegate.h
@@ -12,6 +12,8 @@ namespace blink {
 // a delegate, as their events will be fired on a Service Worker instead.
 class WebNotificationDelegate {
 public:
+    virtual ~WebNotificationDelegate() {}
+
     virtual void dispatchClickEvent() = 0;
     virtual void dispatchShowEvent() = 0;
     virtual void dispatchErrorEvent() = 0;