Move CSSRuleList to the garbage collected heap

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index f12e57867810d217ab1d1453594fd8c6fa8c2af4..d8e95cfa40e291b5308cc90f4ccb39d50d0fb7f6 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -556,7 +556,9 @@ Document::~Document()
     m_timeline->detachFromDocument();
     m_transitionTimeline->detachFromDocument();
 
-    m_styleEngine.clear(); // We need to destory CSSFontSelector before destroying m_fetcher.
+    // We need to destroy CSSFontSelector before destroying m_fetcher.
+    if (m_styleEngine)
+        m_styleEngine->detachFromDocument();
 
     if (m_elemSheet)
         m_elemSheet->clearOwnerNode();