Implement contextmenu attribute with basic support of <menu>

Source/core/page/CustomContextMenuProvider.h

Index: Source/core/page/CustomContextMenuProvider.h
diff --git a/Source/core/page/CustomContextMenuProvider.h b/Source/core/page/CustomContextMenuProvider.h
new file mode 100644
index 0000000000000000000000000000000000000000..cb1022164cbf19966846ea2f651c3822ce3e1d41
--- /dev/null
+++ b/Source/core/page/CustomContextMenuProvider.h
@@ -0,0 +1,42 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CustomContextMenuProvider_h
+#define CustomContextMenuProvider_h
+
+#include "core/page/ContextMenuProvider.h"
+#include "platform/ContextMenuItem.h"
+#include "platform/heap/Handle.h"
+
+namespace blink {
+
+class ContextMenu;
+class HTMLElement;
+class HTMLMenuElement;
+
+class CustomContextMenuProvider FINAL : public ContextMenuProvider {
+public:
+    static PassRefPtr<CustomContextMenuProvider> create(HTMLMenuElement& menu, HTMLElement& subject)
+    {
+        return adoptRef(new CustomContextMenuProvider(menu, subject));
+    }
+
+private:
+    CustomContextMenuProvider(HTMLMenuElement&, HTMLElement&);
+    virtual ~CustomContextMenuProvider();
+
+    virtual void populateContextMenu(ContextMenu*) OVERRIDE;
+    virtual void contextMenuItemSelected(const ContextMenuItem*) OVERRIDE;
+    virtual void contextMenuCleared() OVERRIDE;
+    void populateContextMenuItems(const HTMLMenuElement&, ContextMenu&);
+    HTMLElement* menuItemAt(unsigned menuId);
+
+    RefPtrWillBePersistent<HTMLMenuElement> m_menu;
+    RefPtrWillBePersistent<HTMLElement> m_subjectElement;
+    WillBePersistentHeapVector<RefPtrWillBeMember<HTMLElement> > m_menuItems;
+};
+
+} // namespace blink
+
+#endif