Fix crash in CSSStyleSheetResource::appendData

third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.h

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * Copyright (C) 2010 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 70 matching lines @@
     PreloadRequestStream* m_requests = nullptr;
     const KURL* m_predictedBaseElementURL = nullptr;
 };
 
 // Each CSSPreloaderResourceClient keeps track of a single CSS resource, and
 // drives a CSSPreloadScanner as raw data arrives for it. This lets us preload
 // @import tags before parsing.
 class CSSPreloaderResourceClient : public StyleSheetResourceClient {
 public:
     CSSPreloaderResourceClient(Resource*, HTMLResourcePreloader*);
+    ~CSSPreloaderResourceClient();
     void notifyFinished(Resource*) override;
     void didAppendFirstData(const CSSStyleSheetResource*) override;
     String debugName() const override { return "CSSPreloaderResourceClient"; }
 
 private:
+    void stopObserving();
     Persistent<Resource> m_resource;
     WeakPersistent<HTMLResourcePreloader> m_preloader;
 };
 
 } // namespace blink
 
 #endif