Oilpan: move page's ValidationMessageClient to the heap.

Source/core/page/ValidationMessageClient.h

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 #ifndef ValidationMessageClient_h
 #define ValidationMessageClient_h
 
+#include "platform/heap/Handle.h"
 #include "wtf/Forward.h"
 
 namespace WebCore {
 
 class Document;
 class Element;
 
-class ValidationMessageClient {
+class ValidationMessageClient : public WillBeGarbageCollectedMixin {
 public:

[tkent, 2014/06/16 12:48:38]

nit: ValidationMessageClient can inherit from GarbageCollectedFinalized.

[sof, 2014/06/16 13:01:26]

It definitely could, but I considered that as mixing implementation with
interface.

[tkent, 2014/06/16 13:03:39]

yeah, it's understandable.  You may land this as is.

     virtual ~ValidationMessageClient() { }
 
     // Show validation message for the specified anchor element. An
     // implementation of this function may hide the message automatically after
     // some period.
     virtual void showValidationMessage(const Element& anchor, const String& message) = 0;
 
     // Hide validation message for the specified anchor if the message for the
     // anchor is already visible.
     virtual void hideValidationMessage(const Element& anchor) = 0;
 
     // Returns true if the validation message for the specified anchor element
     // is visible.
     virtual bool isValidationMessageVisible(const Element& anchor) = 0;
 
     virtual void documentDetached(const Document&) = 0;
 
     virtual void willBeDestroyed() = 0;
+
+    virtual void trace(Visitor*) { }
 };
 
 }
 
 #endif