Oilpan: Prepare moving DateTimeChooser to Oilpan

Source/platform/DateTimeChooserClient.h

Index: Source/platform/DateTimeChooserClient.h
diff --git a/Source/platform/DateTimeChooserClient.h b/Source/platform/DateTimeChooserClient.h
index 0cc3d190e35d7a92c68ba2282f0d02ffcde8bf07..e4f6123614ea9a709044e1ebf38f672f2f62c116 100644
--- a/Source/platform/DateTimeChooserClient.h
+++ b/Source/platform/DateTimeChooserClient.h
@@ -32,20 +32,22 @@
 #define DateTimeChooserClient_h
 
 #include "platform/PlatformExport.h"
+#include "platform/heap/Handle.h"
 #include "wtf/text/WTFString.h"
 
 namespace WebCore {
 
-class PLATFORM_EXPORT DateTimeChooserClient {
+class PLATFORM_EXPORT DateTimeChooserClient : public WillBeGarbageCollectedMixin {
+    DECLARE_EMPTY_VIRTUAL_DESTRUCTOR_WILL_BE_REMOVED(DateTimeChooserClient);
 public:
-    virtual ~DateTimeChooserClient();
-
     // Called when user picked a value.
     virtual void didChooseValue(const String&) = 0;
     // Called when user picked a value.
     virtual void didChooseValue(double) = 0;
     // Called when chooser has ended.
     virtual void didEndChooser() = 0;
+
+    virtual void trace(Visitor*) { }
 };
 
 } // namespace WebCore