bug 1262563 - fix how FireShowHideEvent gets the parent of a hide event target r=davidb

Especially for hide events its better to use the parent stored in the event
than the parent of the object when the event is fired.  However xul trees fire
show / hide events where the event's type is AccEvent not a subtype of
AccMutationEvent, and in that case we need to fall back to the objects parent.

accessible/atk/AccessibleWrap.cpp

@@ -1354,16 +1354,29 @@ AccessibleWrap::HandleAccEvent(AccEvent* aEvent)
         break;
 
     case nsIAccessibleEvent::EVENT_SHOW:
-        return FireAtkShowHideEvent(atkObj, true, aEvent->IsFromUserInput());
+      {
+        AccMutationEvent* event = downcast_accEvent(aEvent);
+        Accessible* parentAcc = event ? event->Parent() : accessible->Parent();
+        AtkObject* parent = AccessibleWrap::GetAtkObject(parentAcc);
+        return FireAtkShowHideEvent(atkObj, parent, true,
+                                    aEvent->IsFromUserInput());
+      }
 
     case nsIAccessibleEvent::EVENT_HIDE:
+      {
         // XXX - Handle native dialog accessibles.
         if (!accessible->IsRoot() && accessible->HasARIARole() &&
             accessible->ARIARole() == roles::DIALOG) {
           guint id = g_signal_lookup("deactivate", MAI_TYPE_ATK_OBJECT);
           g_signal_emit(atkObj, id, 0);
         }
-        return FireAtkShowHideEvent(atkObj, false, aEvent->IsFromUserInput());
+
+        AccMutationEvent* event = downcast_accEvent(aEvent);
+        Accessible* parentAcc = event ? event->Parent() : accessible->Parent();
+        AtkObject* parent = AccessibleWrap::GetAtkObject(parentAcc);
+        return FireAtkShowHideEvent(atkObj, parent, false,
+                                    aEvent->IsFromUserInput());
+      }
 
         /*
          * Because dealing with menu is very different between nsIAccessible
@@ -1577,15 +1590,14 @@ static const char *kMutationStrings[2][2] = {
 };
 
 nsresult
-AccessibleWrap::FireAtkShowHideEvent(AtkObject* aObject, bool aIsAdded,
-                                     bool aFromUser)
+AccessibleWrap::FireAtkShowHideEvent(AtkObject* aObject, AtkObject* aParent,
+                                     bool aIsAdded, bool aFromUser)
 {
     int32_t indexInParent = getIndexInParentCB(aObject);
-    AtkObject *parentObject = getParentCB(aObject);
-    NS_ENSURE_STATE(parentObject);
+    NS_ENSURE_STATE(aParent);
 
     const char *signal_name = kMutationStrings[aFromUser][aIsAdded];
-    g_signal_emit_by_name(parentObject, signal_name, indexInParent, aObject, nullptr);
+    g_signal_emit_by_name(aParent, signal_name, indexInParent, aObject, nullptr);
 
     return NS_OK;
 }

accessible/atk/AccessibleWrap.h

@@ -79,8 +79,8 @@ protected:
 
   nsresult FireAtkStateChangeEvent(AccEvent* aEvent, AtkObject *aObject);
   nsresult FireAtkTextChangedEvent(AccEvent* aEvent, AtkObject *aObject);
-  nsresult FireAtkShowHideEvent(AtkObject *aObject, bool aIsAdded,
-                                bool aFromUser);
+  nsresult FireAtkShowHideEvent(AtkObject *aObject, AtkObject* aParent,
+                                bool aIsAdded, bool aFromUser);
 
   AtkObject *mAtkObject;