Implement contextmenu attribute with basic support of <menu>

Source/core/html/HTMLMenuitemElement.h

Index: Source/core/html/HTMLMenuitemElement.h
diff --git a/Source/core/html/HTMLPictureElement.h b/Source/core/html/HTMLMenuitemElement.h
similarity index 52%
copy from Source/core/html/HTMLPictureElement.h
copy to Source/core/html/HTMLMenuitemElement.h
index 0ec61ade8af3ba2786bb29ec2dbb898fa2efa0a4..19c7705e958f568308e94992ca106492ac92063b 100644
--- a/Source/core/html/HTMLPictureElement.h
+++ b/Source/core/html/HTMLMenuitemElement.h
@@ -2,19 +2,19 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef HTMLPictureElement_h
-#define HTMLPictureElement_h
+#ifndef HTMLMenuitemElement_h
+#define HTMLMenuitemElement_h
 
 #include "core/html/HTMLElement.h"
 
 namespace WebCore {
 
-class HTMLPictureElement FINAL : public HTMLElement {
+class HTMLMenuitemElement FINAL : public HTMLElement {
 public:
-    static PassRefPtr<HTMLPictureElement> create(Document&);
+    static PassRefPtr<HTMLMenuitemElement> create(Document&);
 
-protected:
-    explicit HTMLPictureElement(Document&);
+private:
+    explicit HTMLMenuitemElement(Document&);
 };
 
 } // namespace