Make sure the FrameAnimatorView is at the bottom

Bug: 1123889
Test: manual. see bug for repro step.
Change-Id: I3f99b00ccb6478a1bdc1dc871827a48e8560911f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2422866Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809414}

ash/public/cpp/frame_header.cc

@@ -345,6 +345,10 @@ void FrameHeader::StartTransitionAnimation(base::TimeDelta duration) {
 // FrameHeader, private:
 
 void FrameHeader::LayoutHeaderInternal() {
+  // The animator's position can change when the frame is moved from overlay.
+  // Make sure the animator view is at the bottom.
+  view_->ReorderChildView(frame_animator_, 0);
+
   bool use_zoom_icons = caption_button_container()->model()->InZoomMode();
   const gfx::VectorIcon& restore_icon = use_zoom_icons
                                             ? kWindowControlDezoomIcon