res/layout/action_bar_with_button.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  ~ Copyright (C) 2018 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
  -->

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="@dimen/car_app_bar_height">

    <TextView
        android:id="@+id/title"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_marginEnd="@dimen/car_keyline_1"
        android:gravity="center_vertical"
        android:textAppearance="@style/TextAppearance.Car.Title2"
        android:text="@string/title"/>

    <FrameLayout
        android:id="@+id/button_container"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_alignParentEnd="true"
        android:layout_marginEnd="@dimen/car_keyline_1"
        android:orientation="horizontal">

        <Button
            android:id="@+id/action_button1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_vertical"
            style="@style/SystemUpdate.ActionBar.Button.Borderless.Colored"
            android:layout_marginEnd="@dimen/action_bar_end_widget_margin_end" />
    </FrameLayout>

    <ProgressBar
        android:id="@+id/progress_bar"
        style="@style/Widget.Car.ProgressBar.Horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:visibility="gone"
        android:indeterminate="true"/>
</RelativeLayout>