Don't cache parsed stylesheet if it wasn't added to the memory cache.

third_party/WebKit/Source/core/fetch/CSSStyleSheetResource.cpp

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller (mueller@kde.org)
     Copyright (C) 2002 Waldo Bastian (bastian@kde.org)
     Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
     Copyright (C) 2004, 2005, 2006 Apple Computer, Inc.
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
     License as published by the Free Software Foundation; either
@@ skipping 167 matching lines @@
 
     return m_parsedStyleSheetCache;
 }
 
 void CSSStyleSheetResource::saveParsedStyleSheet(StyleSheetContents* sheet)
 {
     ASSERT(sheet && sheet->isCacheable());
 
     if (m_parsedStyleSheetCache)
         m_parsedStyleSheetCache->removedFromMemoryCache();
+
+    if (!memoryCache()->contains(this)) {
+        // This stylesheet resource did conflict with another resource and was
+        // not added to the cache.
+        m_parsedStyleSheetCache = nullptr;
+        return;
+    }
     m_parsedStyleSheetCache = sheet;
+    m_parsedStyleSheetCache->addedToMemoryCache();
 
     setDecodedSize(m_parsedStyleSheetCache->estimatedSizeInBytes());
-
-    // Check if this stylesheet resource didn't conflict with
-    // another resource and has indeed been added to the cache.
-    if (memoryCache()->contains(this))
-        m_parsedStyleSheetCache->addedToMemoryCache();
 }
 
 } // namespace blink