chrome/android/java/res/drawable-v21/web_notification_button_background.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright 2015 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. -->

<ripple xmlns:android="http://schemas.android.com/apk/res/android"
    android:color="@color/ripple_material_light">
    <item android:id="@android:id/mask"
          android:drawable="@drawable/button_compat_shape" />
</ripple>