Bug 266890. Remove nsListboxScrollPortFrame by moving its functionality into nsListBoxFrame. Part of an ongoing effort to remove nsScrollboxFrame and its subclasses. r+sr=bryner

layout/base/nsLayoutUtils.cpp

@@ -349,6 +349,23 @@ nsLayoutUtils::FindSiblingViewFor(nsIView* aParentView, nsIFrame* aFrame) {
   return nsnull;
 }
 
+//static
+nsIScrollableFrame*
+nsLayoutUtils::GetScrollableFrameFor(nsIFrame *aScrolledFrame)
+{
+  nsIFrame *frame = aScrolledFrame->GetParent();
+  if (!frame) {
+    return nsnull;
+  }
+  frame = frame->GetParent();
+  if (!frame) {
+    return nsnull;
+  }
+  nsIScrollableFrame *sf;
+  CallQueryInterface(frame, &sf);
+  return sf;
+}
+
 //static
 nsIScrollableFrame*
 nsLayoutUtils::GetScrollableFrameFor(nsIScrollableView *aScrollableView)