Implement contextmenu attribute with basic support of <menu>

Source/core/html/HTMLMenuElement.h

Index: Source/core/html/HTMLMenuElement.h
diff --git a/Source/core/html/HTMLMenuElement.h b/Source/core/html/HTMLMenuElement.h
index 07350e282252796156e4210a88b80d0c22e20cd1..d54b87f601e516257141f5fa18097c5d525cbe43 100644
--- a/Source/core/html/HTMLMenuElement.h
+++ b/Source/core/html/HTMLMenuElement.h
@@ -23,16 +23,34 @@
 #ifndef HTMLMenuElement_h
 #define HTMLMenuElement_h
 
+#include "core/html/CustomContextMenuProvider.h"
 #include "core/html/HTMLElement.h"
+#include "core/page/ContextMenuProvider.h"
+#include "platform/ContextMenu.h"
+#include "platform/ContextMenuItem.h"
 
 namespace WebCore {
 
+class HTMLMenuElement;
+class CustomContextMenuProvider;
+
 class HTMLMenuElement FINAL : public HTMLElement {
 public:
     static PassRefPtrWillBeRawPtr<HTMLMenuElement> create(Document&);
 
+    virtual void defaultEventHandler(Event*) OVERRIDE;
+
+    CustomContextMenuProvider* menuProvider() { return m_menuProvider.get(); }
+    CustomContextMenuProvider& ensureMenuProvider();
+    void populateContextMenuItems(HTMLMenuElement*, ContextMenu&);
+    HTMLElement* menuItemAt(unsigned menuId);
+    HTMLElement * subjectElement() { return m_subject.get(); }
+
 private:
     explicit HTMLMenuElement(Document&);
+    RefPtr<CustomContextMenuProvider> m_menuProvider;
+    RefPtr<HTMLElement> m_subject;
+    Vector<HTMLElement*> m_menuItems;
 };
 
 } //namespace