Oilpan: move page's ValidationMessageClient to the heap.

Source/core/page/ValidationMessageClient.h

Index: Source/core/page/ValidationMessageClient.h
diff --git a/Source/core/page/ValidationMessageClient.h b/Source/core/page/ValidationMessageClient.h
index bb4d009628c92c43c363211277eca4ba112ed1e8..ae2354cd578779bb3d6a26f62cf3ae61fd1db157 100644
--- a/Source/core/page/ValidationMessageClient.h
+++ b/Source/core/page/ValidationMessageClient.h
@@ -26,6 +26,7 @@
 #ifndef ValidationMessageClient_h
 #define ValidationMessageClient_h
 
+#include "platform/heap/Handle.h"
 #include "wtf/Forward.h"
 
 namespace WebCore {
@@ -33,7 +34,7 @@ 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() { }
 
@@ -53,6 +54,8 @@ public:
     virtual void documentDetached(const Document&) = 0;
 
     virtual void willBeDestroyed() = 0;
+
+    virtual void trace(Visitor*) { }
 };
 
 }