packages/SystemUI/res/layout/car_navigation_bar.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
**
** Copyright 2016, The Android Open Source Project
**
** Licensed under the Apache License, Version 2.0 (the "License");
** you may not use this file except in compliance with the License.
** You may obtain a copy of the License at
**
**     http://www.apache.org/licenses/LICENSE-2.0
**
** Unless required by applicable law or agreed to in writing, software
** distributed under the License is distributed on an "AS IS" BASIS,
** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
** See the License for the specific language governing permissions and
** limitations under the License.
*/
-->

<com.android.systemui.statusbar.car.CarNavigationBarView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:background="@drawable/system_bar_background">

    <!-- phone.NavigationBarView has rot0 and rot90 but we expect the car head unit to have a fixed
         rotation so skip this level of the heirarchy.
    -->
    <LinearLayout
        android:layout_height="match_parent"
        android:layout_width="match_parent"
        android:orientation="horizontal"
        android:clipChildren="false"
        android:clipToPadding="false"
        android:id="@+id/nav_buttons"
        android:animateLayoutChanges="true">

        <!-- Buttons get populated here from a car_arrays.xml. -->
    </LinearLayout>

    <!-- lights out layout to match exactly -->
    <LinearLayout
        android:layout_height="match_parent"
        android:layout_width="match_parent"
        android:orientation="horizontal"
        android:id="@+id/lights_out"
        android:visibility="gone">
        <!-- Must match nav_buttons. -->
    </LinearLayout>

</com.android.systemui.statusbar.car.CarNavigationBarView>