Move CSSRuleList to the garbage collected heap

Source/core/css/CSSImportRule.cpp

Index: Source/core/css/CSSImportRule.cpp
diff --git a/Source/core/css/CSSImportRule.cpp b/Source/core/css/CSSImportRule.cpp
index a552f7b9560a87ea6a8dc330c7c0c5684ffae14b..2192f74227005aab62c0796781d71348f22a3c1e 100644
--- a/Source/core/css/CSSImportRule.cpp
+++ b/Source/core/css/CSSImportRule.cpp
@@ -38,8 +38,6 @@ CSSImportRule::CSSImportRule(StyleRuleImport* importRule, CSSStyleSheet* parent)
 
 CSSImportRule::~CSSImportRule()
 {
-    if (m_styleSheetCSSOMWrapper)
-        m_styleSheetCSSOMWrapper->clearOwnerRule();
 #if !ENABLE(OILPAN)
     // MediaList and the parent CSSImportRule are both on the oilpan heap and die together.
     // Therefor clearing is not needed nor allowed since it could be touching already
@@ -100,6 +98,7 @@ void CSSImportRule::trace(Visitor* visitor)
 {
     visitor->trace(m_importRule);
     visitor->trace(m_mediaCSSOMWrapper);
+    visitor->trace(m_styleSheetCSSOMWrapper);
     CSSRule::trace(visitor);
 }