Bug 1593366 - Check default prevented status in nsListControlFrame::KeyDown. r=mats

Differential Revision: https://phabricator.services.mozilla.com/D51982

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

layout/forms/nsListControlFrame.cpp

@@ -1968,11 +1968,9 @@ nsresult nsListControlFrame::KeyDown(dom::Event* aKeyEvent) {
 
   AutoIncrementalSearchResetter incrementalSearchResetter;
 
-  // Don't check defaultPrevented value because other browsers don't prevent
-  // the key navigation of list control even if preventDefault() is called.
-  // XXXmats 2015-04-16: the above is not true anymore, Chrome prevents all
-  // XXXmats keyboard events, even tabbing, when preventDefault() is called
-  // XXXmats in onkeydown. That seems sub-optimal though.
+  if (aKeyEvent->DefaultPrevented()) {
+    return NS_OK;
+  }
 
   const WidgetKeyboardEvent* keyEvent =
       aKeyEvent->WidgetEventPtr()->AsKeyboardEvent();

layout/forms/test/test_select_prevent_default.html

@@ -49,10 +49,12 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=291082
         previousValue = element.value;
         otherKeys.forEach(function(key) {
           sendKey(key);
-          isnot(element.value, previousValue, "value should have changed while testing key " + key + " (id: " + id + ")");
+          // All these preventDefault on key down in various ways.
+          let shouldchange = id != "keydown" && id != "one" && id != "three";
+          (shouldchange ? isnot : is)(element.value, previousValue, "value should " + (shouldchange ? "" : "not ") + "have changed while testing key " + key + " (id: " + id + ")");
           previousValue = element.value;
-          });
         });
+      });
       SimpleTest.finish();
     });
   }