Add DataPersistent<> for copy-on-modify and use for StyleFilterData.

third_party/WebKit/Source/core/style/StyleFilterData.h

Index: third_party/WebKit/Source/core/style/StyleFilterData.h
diff --git a/third_party/WebKit/Source/core/style/StyleFilterData.h b/third_party/WebKit/Source/core/style/StyleFilterData.h
index e6f254c323bfbfb2d67db86c803f421522d8ae38..f779a194dad9478afc33725d642b5476b4671c03 100644
--- a/third_party/WebKit/Source/core/style/StyleFilterData.h
+++ b/third_party/WebKit/Source/core/style/StyleFilterData.h
@@ -28,15 +28,10 @@
 
 #include "platform/graphics/filters/FilterOperations.h"
 #include "platform/heap/Handle.h"
-#include "wtf/PassRefPtr.h"
-#include "wtf/RefCounted.h"
 
 namespace blink {
 
-// FIXME: Oilpan: resorting to RefCountedGarbageCollected<> here so as to support
-// DataRef<StyleFilterData> uses. Once/if DataRef<> is able to move away from
-// relying on RefPtr<>, switch to GarbageCollected<>.
-class StyleFilterData final : public RefCountedGarbageCollected<StyleFilterData> {
+class StyleFilterData final : public GarbageCollected<StyleFilterData> {
 public:
     static StyleFilterData* create()
     {
@@ -68,5 +63,4 @@ private:
 
 } // namespace blink
 
-
 #endif // StyleFilterData_h