Bug 1051136 - Use editor.canUndo instead of checking the DOM element to see if undos are possible. r=mratcliffe

browser/devtools/projecteditor/test/browser_projecteditor_menubar_02.js

@@ -98,7 +98,11 @@ let test = asyncTest(function*() {
   is (cmdSave.getAttribute("disabled"), "", "File menu item is enabled");
   is (cmdSaveas.getAttribute("disabled"), "", "File menu item is enabled");
 
-  is (cmdUndo.getAttribute("disabled"), "", "Edit menu item is enabled");
+  // Use editor.canUndo() to see if this is failing - the menu disabled property
+  // should be in sync with this because of isCommandEnabled in editor.js.
+  info ('cmdUndo.getAttribute("disabled") is: "' + cmdUndo.getAttribute("disabled") + '"');
+  ok (editor.editor.canUndo(), "Edit menu item is enabled");
+
   is (cmdRedo.getAttribute("disabled"), "true", "Edit menu item is disabled");
   is (cmdCut.getAttribute("disabled"), "true", "Edit menu item is disabled");
   is (cmdCopy.getAttribute("disabled"), "true", "Edit menu item is disabled");