StyleSheet.ownerNode should be null when it gets orphaned.

Source/core/html/HTMLLinkElement.cpp

Index: Source/core/html/HTMLLinkElement.cpp
diff --git a/Source/core/html/HTMLLinkElement.cpp b/Source/core/html/HTMLLinkElement.cpp
index a98eaa0e76d795d7b82e483736bba3fb9f629a90..a1ed6927d9af6a0da0c665650c7c55e78b51594e 100644
--- a/Source/core/html/HTMLLinkElement.cpp
+++ b/Source/core/html/HTMLLinkElement.cpp
@@ -406,6 +406,8 @@ void LinkStyle::setCSSStyleSheet(const String& href, const KURL& baseURL, const
         ASSERT(restoredSheet->isCacheable());
         ASSERT(!restoredSheet->isLoading());
 
+        if (m_sheet)
+            clearSheet();
         m_sheet = CSSStyleSheet::create(restoredSheet, m_owner);
         m_sheet->setMediaQueries(MediaQuerySet::create(m_owner->media()));
         m_sheet->setTitle(m_owner->title());
@@ -418,6 +420,8 @@ void LinkStyle::setCSSStyleSheet(const String& href, const KURL& baseURL, const
 
     RefPtr<StyleSheetContents> styleSheet = StyleSheetContents::create(href, parserContext);
 
+    if (m_sheet)
+        clearSheet();
     m_sheet = CSSStyleSheet::create(styleSheet, m_owner);
     m_sheet->setMediaQueries(MediaQuerySet::create(m_owner->media()));
     m_sheet->setTitle(m_owner->title());