Remove more oilpan.

sky/engine/core/dom/MutationObserverRegistration.h

Index: sky/engine/core/dom/MutationObserverRegistration.h
diff --git a/sky/engine/core/dom/MutationObserverRegistration.h b/sky/engine/core/dom/MutationObserverRegistration.h
index 688a31b3265626cf0e828d9c2de40c44f1becce5..34a158c0901a3e5179475518c1f36d03a5bdd0c9 100644
--- a/sky/engine/core/dom/MutationObserverRegistration.h
+++ b/sky/engine/core/dom/MutationObserverRegistration.h
@@ -41,7 +41,7 @@ namespace blink {
 
 class QualifiedName;
 
-class MutationObserverRegistration final : public DummyBase<MutationObserverRegistration> {
+class MutationObserverRegistration final {
 public:
     static PassOwnPtr<MutationObserverRegistration> create(MutationObserver&, Node*, MutationObserverOptions, const HashSet<AtomicString>& attributeFilter);
     ~MutationObserverRegistration();