chrome/android/java/res/drawable/file_picker_scrim.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright 2017 The Chromium Authors. All rights reserved.
     Use of this source code is governed by a BSD-style license that can be
     found in the LICENSE file. -->

<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <gradient
        android:startColor="@color/black_alpha_30"
        android:endColor="@android:color/transparent"
        android:type="radial"
        android:gradientRadius="64dp"
        android:centerY="0%"
        android:centerX="0%" />
</shape>