[Oilpan]: Make StylePropertySet fully garbage collected.

Source/core/css/resolver/StyleResolver.cpp

Index: Source/core/css/resolver/StyleResolver.cpp
diff --git a/Source/core/css/resolver/StyleResolver.cpp b/Source/core/css/resolver/StyleResolver.cpp
index 5c412c674ed019f230ad475fbccdcba2dba638f4..931b92a3ac07b6a5aff0d656b8c7b66efa5fbacb 100644
--- a/Source/core/css/resolver/StyleResolver.cpp
+++ b/Source/core/css/resolver/StyleResolver.cpp
@@ -106,7 +106,7 @@ RenderStyle* StyleResolver::s_styleNotYetAvailable;
 
 static StylePropertySet* leftToRightDeclaration()
 {
-    DEFINE_STATIC_REF(MutableStylePropertySet, leftToRightDecl, (MutableStylePropertySet::create()));
+    DEFINE_STATIC_REF_WILL_BE_PERSISTENT(MutableStylePropertySet, leftToRightDecl, (MutableStylePropertySet::create()));
     if (leftToRightDecl->isEmpty())
         leftToRightDecl->setProperty(CSSPropertyDirection, CSSValueLtr);
     return leftToRightDecl;
@@ -114,7 +114,7 @@ static StylePropertySet* leftToRightDeclaration()
 
 static StylePropertySet* rightToLeftDeclaration()
 {
-    DEFINE_STATIC_REF(MutableStylePropertySet, rightToLeftDecl, (MutableStylePropertySet::create()));
+    DEFINE_STATIC_REF_WILL_BE_PERSISTENT(MutableStylePropertySet, rightToLeftDecl, (MutableStylePropertySet::create()));
     if (rightToLeftDecl->isEmpty())
         rightToLeftDecl->setProperty(CSSPropertyDirection, CSSValueRtl);
     return rightToLeftDecl;
@@ -1495,6 +1495,7 @@ bool StyleResolver::mediaQueryAffectedByViewportChange() const
 void StyleResolver::trace(Visitor* visitor)
 {
     visitor->trace(m_keyframesRuleMap);
+    visitor->trace(m_matchedPropertiesCache);
     visitor->trace(m_viewportDependentMediaQueryResults);
     visitor->trace(m_viewportStyleResolver);
     visitor->trace(m_siblingRuleSet);