chromium/components/browser_ui/styles/android/java/res/drawable/circle_white.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
Copyright 2017 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="20dp"
        android:width="20dp"/>
    <stroke
        android:width="2dp"
        android:color="@android:color/white"/>
</shape>