chromium/chrome/browser/resources/side_panel/read_anything/menus/line_spacing_menu.html

<simple-action-menu
    id="menu"
    label="$i18n{lineSpacingTitle}"
    event-name="[[toolbarEventEnum_.LINE_SPACING]]"
    menu-items="[[options_]]"
    current-selected-index="[[restoredLineSpacingIndex_(settingsPrefs)]]"
    on-line-spacing-change="onLineSpacingChange_"
    initial-count="3">
</simple-action-menu>