Merge "Keep wallpaper in prepare back transition." into main

                int rootIdx = -1;

                for (int i = info.getChanges().size() - 1; i >= 0; --i) {

                    final TransitionInfo.Change c = info.getChanges().get(i);

                    if (c.hasFlags(FLAG_IS_WALLPAPER)) {

                        st.setAlpha(c.getLeash(), 1.0f);

                        continue;

                    }

                    if (TransitionUtil.isOpeningMode(c.getMode())) {

                        final Point offset = c.getEndRelOffset();

                        st.setPosition(c.getLeash(), offset.x, offset.y);