Implement disabled and checked attribute for menuitem.

LayoutTests/fast/dom/HTMLMenuElement/custom-context-menu.html

Index: LayoutTests/fast/dom/HTMLMenuElement/custom-context-menu.html
diff --git a/LayoutTests/fast/dom/HTMLMenuElement/custom-context-menu.html b/LayoutTests/fast/dom/HTMLMenuElement/custom-context-menu.html
index e1d311ffa4eba27f674f3e426e9c042cfdb061c1..e565c5c9ee902abdb8f285915d555011e943c78d 100644
--- a/LayoutTests/fast/dom/HTMLMenuElement/custom-context-menu.html
+++ b/LayoutTests/fast/dom/HTMLMenuElement/custom-context-menu.html
@@ -9,7 +9,8 @@
         <!-- Test removal of separator at the start. -->
         <hr>
         <menuitem label="Item1"></menuitem>
-        <menuitem label="Item2"></menuitem>
+        <!-- Test disabled menuitem. -->
+        <menuitem label="Item2" disabled></menuitem>
         <!-- Test addition of separator for <hr>. -->
         <hr>
         <menuitem label="Item3"></menuitem>
@@ -138,7 +139,7 @@ var items4 = contextClickAndGetMenuItems(button4);
 
 shouldBeEqualToNumber("itemsWithCustomContextMenu.length - items.length", 17);
 shouldBeEqualToString("itemsWithCustomContextMenu[0]", "Item1");
-shouldBeEqualToString("itemsWithCustomContextMenu[1]", "Item2");
+shouldBeEqualToString("itemsWithCustomContextMenu[1]", "#Item2");
 shouldBeEqualToString("itemsWithCustomContextMenu[2]", "---------");
 shouldBeEqualToString("itemsWithCustomContextMenu[3]", "Item3");
 shouldBeEqualToString("itemsWithCustomContextMenu[4]", "Submenu >");