packages/SystemUI/res/layout/window_magnifier_view.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  ~ Copyright (C) 2019 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="wrap_content"
    android:layout_height="wrap_content">

    <SurfaceView
        android:layout_marginStart="@dimen/magnification_border_size"
        android:layout_marginTop="@dimen/magnification_border_size"
        android:id="@+id/surface_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <View
            android:id="@+id/left_handle"
            android:layout_width="@dimen/magnification_border_size"
            android:layout_height="match_parent"
            android:layout_above="@+id/drag_handle"
            android:background="@color/magnification_border_color" />

        <View
            android:id="@+id/top_handle"
            android:layout_width="match_parent"
            android:layout_height="@dimen/magnification_border_size"
            android:background="@color/magnification_border_color" />

        <View
            android:id="@+id/right_handle"
            android:layout_width="@dimen/magnification_border_size"
            android:layout_height="match_parent"
            android:layout_above="@+id/drag_handle"
            android:layout_alignParentEnd="true"
            android:background="@color/magnification_border_color" />

        <View
            android:id="@+id/bottom_handle"
            android:layout_width="match_parent"
            android:layout_height="@dimen/magnification_border_size"
            android:layout_above="@+id/drag_handle"
            android:background="@color/magnification_border_color" />

        <View
            android:id="@+id/drag_handle"
            android:layout_width="@dimen/magnification_drag_view_width"
            android:layout_height="@dimen/magnification_drag_view_height"
            android:layout_alignParentBottom="true"
            android:layout_centerHorizontal="true"
            android:background="@color/magnification_border_color" />

    </RelativeLayout>
</FrameLayout>