alternate ntp: fix website page jankiness when suggestions show and top bars are hidden

chrome/browser/ui/views/frame/contents_container.cc

Index: chrome/browser/ui/views/frame/contents_container.cc
diff --git a/chrome/browser/ui/views/frame/contents_container.cc b/chrome/browser/ui/views/frame/contents_container.cc
index 3af337b2c7abc59064ac6667c17e9d6226df0b87..7da065cb0861a8adb03248acbd01e9a95798bcc1 100644
--- a/chrome/browser/ui/views/frame/contents_container.cc
+++ b/chrome/browser/ui/views/frame/contents_container.cc
@@ -175,6 +175,10 @@ void ContentsContainer::MaybeStackPreviewAtTop() {
   Layout();
 }
 
+int ContentsContainer::preview_height() const {
+  return preview_ ? preview_->bounds().height() : 0;
+}
+
 void ContentsContainer::SetActiveTopMargin(int margin) {
   if (active_top_margin_ == margin)
     return;