b=835044 handle popup windows with parents in GetWidgetOffset r=tn

level="parent" popup windows can sometimes return a non-null parent, which is
their owner window, but their bounds are relative to the screen (previously
assumed to be the owner window origin).

--HG--
extra : transplant_source : %AEr%1F%1E%CC%08%A1%19%97%DBo%00f%5E%3EM%23R%FE%95

layout/base/nsLayoutUtils.cpp

@@ -2308,13 +2308,16 @@ nsLayoutUtils::TransformFrameRectToAncestor(nsIFrame* aFrame,
 
 static nsIntPoint GetWidgetOffset(nsIWidget* aWidget, nsIWidget*& aRootWidget) {
   nsIntPoint offset(0, 0);
-  nsIWidget* parent = aWidget->GetParent();
-  while (parent) {
+  while ((aWidget->WindowType() == eWindowType_child ||
+          aWidget->WindowType() == eWindowType_plugin)) {
+    nsIWidget* parent = aWidget->GetParent();
+    if (!parent) {
+      break;
+    }
     nsIntRect bounds;
     aWidget->GetBounds(bounds);
     offset += bounds.TopLeft();
     aWidget = parent;
-    parent = aWidget->GetParent();
   }
   aRootWidget = aWidget;
   return offset;