Fix formAction return value for empty formaction content attribute.

Source/core/html/HTMLInputElement.idl

Index: Source/core/html/HTMLInputElement.idl
diff --git a/Source/core/html/HTMLInputElement.idl b/Source/core/html/HTMLInputElement.idl
index cdaed213535a8b7801884bb6f0918d0e3e3d12a3..b82f0960df07787dbdeb3676b5a707bfb51cc24c 100644
--- a/Source/core/html/HTMLInputElement.idl
+++ b/Source/core/html/HTMLInputElement.idl
@@ -36,7 +36,7 @@ interface HTMLInputElement : HTMLElement {
     // The 'files' attribute is intentionally not readonly.
     // https://www.w3.org/Bugs/Public/show_bug.cgi?id=22682
     attribute FileList? files;
-    [Reflect, URL] attribute DOMString formAction;
+    attribute DOMString formAction;
     [CustomElementCallbacks] attribute DOMString formEnctype;
     [CustomElementCallbacks] attribute DOMString formMethod;
     [Reflect] attribute boolean formNoValidate;