Fix crash in CSSStyleSheetResource::appendData

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

Index: third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.h
diff --git a/third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.h b/third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.h
index 9117b08c3df9761800f35a2520566af23a98033d..af3a8f302e9d2e5d630ff896bf0cd1d1b0c7642c 100644
--- a/third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.h
+++ b/third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.h
@@ -88,11 +88,13 @@ private:
 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;
 };