Fix FontFaceSet state getting stuck at loading

third_party/WebKit/Source/core/css/FontFace.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 83 matching lines @@
     void setError(DOMException* = nullptr);
     DOMException* error() const { return m_error; }
     FontTraits traits() const;
     CSSFontFace* cssFontFace() { return m_cssFontFace.get(); }
     size_t approximateBlankCharacterCount() const;
 
     DECLARE_VIRTUAL_TRACE();
 
     bool hadBlankText() const;
 
-    class LoadFontCallback : public GarbageCollectedFinalized<LoadFontCallback> {
+    class LoadFontCallback : public GarbageCollectedMixin {
     public:
         virtual ~LoadFontCallback() { }
         virtual void notifyLoaded(FontFace*) = 0;
         virtual void notifyError(FontFace*) = 0;
         DEFINE_INLINE_VIRTUAL_TRACE() { }
     };
     void loadWithCallback(LoadFontCallback*, ExecutionContext*);
+    void addCallback(LoadFontCallback*);
 
     // ScriptWrappable:
     bool hasPendingActivity() const final;
 
 private:
     static FontFace* create(ExecutionContext*, const AtomicString& family, DOMArrayBuffer* source, const FontFaceDescriptors&);
     static FontFace* create(ExecutionContext*, const AtomicString& family, DOMArrayBufferView*, const FontFaceDescriptors&);
     static FontFace* create(ExecutionContext*, const AtomicString& family, const String& source, const FontFaceDescriptors&);
 
     explicit FontFace(ExecutionContext*);
@@ skipping 25 matching lines @@
     Member<LoadedProperty> m_loadedProperty;
     Member<CSSFontFace> m_cssFontFace;
     HeapVector<Member<LoadFontCallback>> m_callbacks;
 };
 
 using FontFaceArray = HeapVector<Member<FontFace>>;
 
 } // namespace blink
 
 #endif // FontFace_h