Have ScriptPromiseResolver on the Oilpan heap always.

Source/core/imagebitmap/ImageBitmapFactories.h

 /*
  * Copyright (c) 2013, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 78 matching lines @@
         void rejectPromise();
 
         // FileReaderLoaderClient
         void didStartLoading() override { }
         void didReceiveData() override { }
         void didFinishLoading() override;
         void didFail(FileError::ErrorCode) override;
 
         FileReaderLoader m_loader;
         RawPtrWillBeMember<ImageBitmapFactories> m_factory;
-        RefPtrWillBeMember<ScriptPromiseResolver> m_resolver;
+        Member<ScriptPromiseResolver> m_resolver;
         IntRect m_cropRect;
     };
 
     static ImageBitmapFactories& from(EventTarget&);
 
     template<class GlobalObject>
     static ImageBitmapFactories& fromInternal(GlobalObject&);
 
     void addLoader(ImageBitmapLoader*);
     void didFinishLoading(ImageBitmapLoader*);
 
     PersistentHeapHashSetWillBeHeapHashSet<Member<ImageBitmapLoader>> m_pendingLoaders;
 };
 
 } // namespace blink
 
 #endif // ImageBitmapFactories_h