res/layout/back_gesture_indicator_container.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
  -->

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="horizontal"
              android:layout_width="match_parent"
              android:layout_height="match_parent">

    <ImageView
        android:layout_width="@dimen/back_gesture_indicator_width"
        android:layout_height="match_parent"
        android:id="@+id/indicator_left">
    </ImageView>

    <Space
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_weight="1" />

    <ImageView
        android:layout_width="@dimen/back_gesture_indicator_width"
        android:layout_height="match_parent"
        android:id="@+id/indicator_right">
    </ImageView>

</LinearLayout>