Fix crash in CSSStyleSheetResource::appendData

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 87 matching lines @@
     // Don't cache the decoded text, regenerating is cheap and it can use quite a bit of memory
     return decodedText();
 }
 
 void CSSStyleSheetResource::appendData(const char* data, size_t length)
 {
     Resource::appendData(data, length);
     if (m_didNotifyFirstData)
         return;
     ResourceClientWalker<StyleSheetResourceClient> w(m_clients);
-    while (StyleSheetResourceClient* c = w.next())
+    while (StyleSheetResourceClient* c = w.next()) {
+        ASSERT(m_data);
         c->didAppendFirstData(this);
+    }
     m_didNotifyFirstData = true;
 }
 
 void CSSStyleSheetResource::checkNotify()
 {
     // Decode the data to find out the encoding and keep the sheet text around during checkNotify()
     if (m_data)
         m_decodedSheetText = decodedText();
 
     ResourceClientWalker<StyleSheetResourceClient> w(m_clients);
@@ skipping 69 matching lines @@
 
     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