Remove TreatNullAs=NullString for HTMLImageElement

LayoutTests/fast/dom/element-attribute-js-null.html

Index: LayoutTests/fast/dom/element-attribute-js-null.html
diff --git a/LayoutTests/fast/dom/element-attribute-js-null.html b/LayoutTests/fast/dom/element-attribute-js-null.html
index 850191ee6ff319863493a1f42de08753d5f9b443..b8eae26e745b134b7a15610872efb195e0f80856 100644
--- a/LayoutTests/fast/dom/element-attribute-js-null.html
+++ b/LayoutTests/fast/dom/element-attribute-js-null.html
@@ -334,14 +334,16 @@
                     type: 'HTMLImageElement',
                     elementToUse: document.createElement('img'),
                     attributes: [
-                        {name: 'name', expectedNull: ''},
-                        {name: 'align', expectedNull: ''},
-                        {name: 'alt', expectedNull: ''},
+                        {name: 'align', expectedNull: 'null'},
+                        {name: 'alt', expectedNull: 'null'},
                         {name: 'border', expectedNull: ''},
-                        {name: 'longDesc', expectedNull: ''},
-                        {name: 'src', expectedNull: ''},
-                        {name: 'useMap', expectedNull: ''},
-                        {name: 'lowsrc', expectedNull: ''}
+                        {name: 'crossOrigin', expectedNull: 'null'},
+                        {name: 'longDesc', expectedNull: 'null', isUrl: true},
+                        {name: 'lowsrc', expectedNull: 'null', isUrl: true},
+                        {name: 'name', expectedNull: 'null'},
+                        {name: 'src', expectedNull: 'null', isUrl: true},
+                        {name: 'srcset', expectedNull: 'null'},
+                        {name: 'useMap', expectedNull: 'null'}
                     ]
                 },
                 {