Add support for [TreatNullAs] extended attribute for reflected attributes

Source/core/html/HTMLMarqueeElement.idl

Index: Source/core/html/HTMLMarqueeElement.idl
diff --git a/Source/core/html/HTMLMarqueeElement.idl b/Source/core/html/HTMLMarqueeElement.idl
index b5bda0cd84722505444c5ef4109483c787845b2e..827da3e9179c88144730d00c12534ae358eaf0b0 100644
--- a/Source/core/html/HTMLMarqueeElement.idl
+++ b/Source/core/html/HTMLMarqueeElement.idl
@@ -21,17 +21,17 @@ interface HTMLMarqueeElement : HTMLElement {
     void start();
     void stop();
 
-    [Reflect] attribute DOMString behavior;
-    [Reflect] attribute DOMString bgColor;
-    [Reflect] attribute DOMString direction;
-    [Reflect] attribute DOMString height;
+    [Reflect, TreatNullAs=NullString] attribute DOMString behavior;
+    [Reflect, TreatNullAs=NullString] attribute DOMString bgColor;
+    [Reflect, TreatNullAs=NullString] attribute DOMString direction;
+    [Reflect, TreatNullAs=NullString] attribute DOMString height;
     [Reflect] attribute unsigned long hspace;
     [SetterRaisesException] attribute long loop;
     [SetterRaisesException] attribute long scrollAmount;
     [SetterRaisesException] attribute long scrollDelay;
     [Reflect] attribute boolean trueSpeed;
     [Reflect] attribute unsigned long vspace;
-    [Reflect] attribute DOMString width;
+    [Reflect, TreatNullAs=NullString] attribute DOMString width;
 
     // FIXME: Implement the following event handler attributes
     // https://bugs.webkit.org/show_bug.cgi?id=49788