Oilpan: Prepare moving DateTimeChooser to Oilpan

Source/platform/DateTimeChooser.h

Index: Source/platform/DateTimeChooser.h
diff --git a/Source/platform/DateTimeChooser.h b/Source/platform/DateTimeChooser.h
index 34ab17061a9baaff9aa3852eef0e57399d6de381..ca5e13c758ec998f21e8fa13b8ea9d8ea7486c2e 100644
--- a/Source/platform/DateTimeChooser.h
+++ b/Source/platform/DateTimeChooser.h
@@ -33,6 +33,7 @@
 
 #include "platform/PlatformExport.h"
 #include "platform/geometry/IntRect.h"
+#include "platform/heap/Handle.h"
 #include "wtf/RefCounted.h"
 #include "wtf/text/WTFString.h"
 
@@ -63,12 +64,12 @@ struct DateTimeChooserParameters {
     bool isAnchorElementRTL;
 };
 
-// For pickers like color pickers and date pickers.
-class PLATFORM_EXPORT DateTimeChooser : public RefCounted<DateTimeChooser> {
+class PLATFORM_EXPORT DateTimeChooser : public RefCountedWillBeGarbageCollectedFinalized<DateTimeChooser> {
 public:
     virtual ~DateTimeChooser();
 
     virtual void endChooser() = 0;
+    virtual void trace(Visitor*) { }
 };
 
 } // namespace WebCore