packages/Shell/res/layout/null_home_finishing_boot.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  ~ Copyright (C) 2020 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
  -->
<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#80000000"
    android:forceHasOverlappingRendering="false">
    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        android:layout_gravity="center"
        android:layout_marginStart="16dp"
        android:layout_marginEnd="16dp">
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="40sp"
            android:textColor="?android:attr/textColorPrimary"
            android:text="@*android:string/android_start_title"/>
        <ProgressBar
            style="@android:style/Widget.Material.ProgressBar.Horizontal"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="12.75dp"
            android:colorControlActivated="?android:attr/textColorPrimary"
            android:indeterminate="true"/>
    </LinearLayout>
</FrameLayout>