Bug 1536241 [wpt PR 15857] - Update interfaces/DOM-Parsing.idl, a=testonly

Automatic update from web-platform-tests
Update interfaces/DOM-Parsing.idl (#15857)

Source: https://github.com/tidoust/reffy-reports/blob/e0218fe/whatwg/idl/DOM-Parsing.idl
Build: https://travis-ci.org/tidoust/reffy-reports/builds/506822321
--

wpt-commits: 488f4440d07c85319ee4f34c1021f69f20e6f9a3
wpt-pr: 15857

testing/web-platform/tests/interfaces/DOM-Parsing.idl

@@ -18,12 +18,18 @@ enum SupportedType {
 
 [Constructor, Exposed=Window]
 
-  interface XMLSerializer {
+interface XMLSerializer {
   DOMString serializeToString(Node root);
 };
 
-partial interface Element {
+interface mixin InnerHTML {
   [CEReactions, TreatNullAs=EmptyString] attribute DOMString innerHTML;
+};
+
+Element includes InnerHTML;
+ShadowRoot includes InnerHTML;
+
+partial interface Element {
   [CEReactions, TreatNullAs=EmptyString] attribute DOMString outerHTML;
   [CEReactions] void insertAdjacentHTML(DOMString position, DOMString text);
 };