Oilpan: prefer eager finalization over prefinalizers.

Source/core/dom/MutationObserver.h

Index: Source/core/dom/MutationObserver.h
diff --git a/Source/core/dom/MutationObserver.h b/Source/core/dom/MutationObserver.h
index 157ce4ca869985ad9e0abf3d62bccfdc183425aa..deda1e3f73b5051d82d59060e8ce8ca228f3e4e3 100644
--- a/Source/core/dom/MutationObserver.h
+++ b/Source/core/dom/MutationObserver.h
@@ -60,7 +60,6 @@ using MutationRecordVector = WillBeHeapVector<RefPtrWillBeMember<MutationRecord>
 
 class MutationObserver final : public RefCountedWillBeGarbageCollectedFinalized<MutationObserver>, public ScriptWrappable {
     DEFINE_WRAPPERTYPEINFO();
-    WILL_BE_USING_PRE_FINALIZER(MutationObserver, dispose);
 public:
     enum MutationType {
         ChildList = 1 << 0,
@@ -96,6 +95,8 @@ public:
 
     WillBeHeapHashSet<RawPtrWillBeMember<Node>> getObservedNodes() const;
 
+    // Eagerly finalized as destructor accesses heap object members.
+    EAGERLY_FINALIZE();
     DECLARE_TRACE();
 
 private:
@@ -105,8 +106,6 @@ private:
     void deliver();
     bool shouldBeSuspended() const;
 
-    void dispose();
-
     OwnPtrWillBeMember<MutationCallback> m_callback;
     MutationRecordVector m_records;
     MutationObserverRegistrationSet m_registrations;