Fix crash in CSSStyleSheetResource::appendData

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

 /*
  * Copyright (C) 2008, 2010 Apple Inc. All Rights Reserved.
  * Copyright (C) 2009 Torch Mobile, Inc. http://www.torchmobile.com/
  * 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.
@@ skipping 219 matching lines @@
         m_state = Initial;
     } else if (equalIgnoringCase(m_rule, "charset"))
         m_state = Initial;
     else
         m_state = DoneParsingImportRules;
     m_rule.clear();
     m_ruleValue.clear();
 }
 
 CSSPreloaderResourceClient::CSSPreloaderResourceClient(Resource* resource, HTMLResourcePreloader* preloader)
-    : m_resource(resource)
-    , m_preloader(preloader)
+    : m_preloader(preloader)
 {
+    ASSERT(resource->getType() == Resource::CSSStyleSheet);
+    setResource(static_cast<CSSStyleSheetResource*>(resource));
 }
 
 void CSSPreloaderResourceClient::notifyFinished(Resource* resource)
 {
-    resource->removeClient(this);
-    m_resource.clear();
+    clearResource();
 }
 
 // Only attach for one appendData call, as that's where most imports will likely
 // be (according to spec).
 void CSSPreloaderResourceClient::didAppendFirstData(const CSSStyleSheetResource* resource)
 {
     const String& chunk = resource->decodedText();
     if (!chunk.isNull() && m_preloader) {
         CSSPreloadScanner cssPreloadScanner;
         PreloadRequestStream preloads;
         // Passing an empty SegmentedString here results in PreloadRequests
         // with no file/line information.
         // TODO(csharrison): If this becomes an issue the CSSPreloadScanner
         // may be augmented to take care of this case without performing an
         // additional copy.
         cssPreloadScanner.scan(chunk, SegmentedString(), preloads, resource->response().url());
         int currentPreloadCount = m_preloader->countPreloads();
         m_preloader->takeAndPreload(preloads);
         DEFINE_STATIC_LOCAL(CustomCountHistogram, cssImportHistogram, ("PreloadScanner.ExternalCSS.PreloadCount", 1, 100, 50));
         cssImportHistogram.count(m_preloader->countPreloads() - currentPreloadCount);
     }
-    m_resource->removeClient(this);
-    m_resource.clear();
+    clearResource();
+}
+
+DEFINE_TRACE(CSSPreloaderResourceClient)
+{
+    visitor->trace(m_preloader);
+    ResourceOwner<StyleSheetResource>::trace(visitor);
 }
 
 } // namespace blink