chromium/components/browser_ui/photo_picker/android/java/res/drawable/photo_picker_seekbar_thumb.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
Copyright 2020 The Chromium Authors
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"
    android:shape="oval">

    <size
        android:height="@dimen/photo_picker_seek_bar_thumb_size"
        android:width="@dimen/photo_picker_seek_bar_thumb_size" />
    <solid android:color="@color/default_primary_color"/>
</shape>