Bug 1492582 - Use XUL inspector highlighter for HTML docs without scroll frames. r=bgrins

The devtools highlighter is broken with browser.xhtml when scroll frames
are disabled.

Differential Revision: https://phabricator.services.mozilla.com/D52104

--HG--
extra : moz-landing-system : lando

devtools/server/actors/highlighters/utils/markup.js

@@ -102,7 +102,14 @@ ClassList.prototype = {
  * @return {Boolean}
  */
 function isXUL(window) {
-  return window.document.documentElement.namespaceURI === XUL_NS;
+  // XXX: We temporarily return true for HTML documents if the document disables
+  // scroll frames since the regular highlighter is broken in this case. This
+  // should be removed when bug 1594587 is fixed.
+  return (
+    window.document.documentElement.namespaceURI === XUL_NS ||
+    (window.isChromeWindow &&
+      window.document.documentElement.getAttribute("scrolling") === "false")
+  );
 }
 exports.isXUL = isXUL;