Making HiddenInputElement implement InputElementBase.

tools/dom/templates/html/impl/impl_HTMLInputElement.darttemplate

Index: tools/dom/templates/html/impl/impl_HTMLInputElement.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_HTMLInputElement.darttemplate b/tools/dom/templates/html/impl/impl_HTMLInputElement.darttemplate
index bcac38d718c815385ecbae66eca6536540e9ff7f..2c3d9a26126218355f62890a259f584453493abc 100644
--- a/tools/dom/templates/html/impl/impl_HTMLInputElement.darttemplate
+++ b/tools/dom/templates/html/impl/impl_HTMLInputElement.darttemplate
@@ -43,8 +43,8 @@ $!MEMBERS
 
 
 // Interfaces representing the InputElement APIs which are supported
-// for the various types of InputElement.
-// From http://dev.w3.org/html5/spec/the-input-element.html#the-input-element.
+// for the various types of InputElement. From:
+// http://www.w3.org/html/wg/drafts/html/master/forms.html#the-input-element.
 
 /**
  * Exposes the functionality common between all InputElement types.
@@ -90,7 +90,7 @@ abstract class InputElementBase implements Element {
 /**
  * Hidden input which is not intended to be seen or edited by the user.
  */
-abstract class HiddenInputElement implements Element {
+abstract class HiddenInputElement implements InputElementBase {
   factory HiddenInputElement() => new InputElement(type: 'hidden');
 }