Oilpan: tidy StylePropertySerializer's handling of GCed objects.

Source/core/css/StylePropertySerializer.h

Index: Source/core/css/StylePropertySerializer.h
diff --git a/Source/core/css/StylePropertySerializer.h b/Source/core/css/StylePropertySerializer.h
index 2a2bfd6a93080b3da55b66a865f46b9f8f5c5b18..3d209d42a5fd98359d53ac1d65ccc247b8ff1760 100644
--- a/Source/core/css/StylePropertySerializer.h
+++ b/Source/core/css/StylePropertySerializer.h
@@ -34,6 +34,7 @@ class StylePropertySet;
 class StylePropertyShorthand;
 
 class StylePropertySerializer {
+    STACK_ALLOCATED();
 public:
     explicit StylePropertySerializer(const StylePropertySet&);
 
@@ -88,7 +89,8 @@ private:
         bool m_isInherited;
     };
 
-    class StylePropertySetForSerializer {
+    class StylePropertySetForSerializer final {
+        DISALLOW_ALLOCATION();
     public:
         explicit StylePropertySetForSerializer(const StylePropertySet&);
 
@@ -101,11 +103,13 @@ private:
         bool isPropertyImplicit(CSSPropertyID) const;
         bool propertyIsImportant(CSSPropertyID) const;
 
+        DECLARE_TRACE();
+
     private:
         bool hasExpandedAllProperty() const { return hasAllProperty() && m_needToExpandAll; }
         bool hasAllProperty() const { return m_allIndex != -1; }
 
-        const StylePropertySet& m_propertySet;
+        RawPtrWillBeMember<const StylePropertySet> m_propertySet;
         int m_allIndex;
         BitArray<numCSSProperties> m_longhandPropertyUsed;
         bool m_needToExpandAll;
@@ -116,4 +120,4 @@ private:
 
 } // namespace blink
 
-#endif
+#endif // StylePropertySerializer_h