chromium/chrome/android/features/tab_ui/java/res/drawable/tab_grid_selection_list_icon.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
Copyright 2019 The Chromium Authors
Use of this source code is governed by a BSD-style license that can be
found in the LICENSE file.
-->

<level-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:maxLevel="@integer/list_item_level_default">
        <shape android:shape="oval">
            <solid android:color="@android:color/transparent"/>
            <stroke
                android:width="2dp"
                android:color="@macro/default_icon_color"/>
        </shape>
    </item>
    <item android:maxLevel="@integer/list_item_level_selected">
        <shape android:shape="oval">
            <solid android:color="@macro/default_control_color_active" />
        </shape>
    </item>
</level-list>