core/res/res/layout/notification_template_part_line2.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  ~ Copyright (C) 2014 The Android Open Source Project
  ~
  ~ Licensed under the Apache License, Version 2.0 (the "License");
  ~ you may not use this file except in compliance with the License.
  ~ You may obtain a copy of the License at
  ~
  ~      http://www.apache.org/licenses/LICENSE-2.0
  ~
  ~ Unless required by applicable law or agreed to in writing, software
  ~ distributed under the License is distributed on an "AS IS" BASIS,
  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  ~ See the License for the specific language governing permissions and
  ~ limitations under the License
  -->

<merge xmlns:android="http://schemas.android.com/apk/res/android">
    <TextView 
        android:id="@+id/text2"
        android:textAppearance="@style/TextAppearance.StatusBar.Material.EventContent.Line2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="-2dp"
        android:layout_marginBottom="-2dp"
        android:singleLine="true"
        android:fadingEdge="horizontal"
        android:ellipsize="marquee"
        android:visibility="gone"
        android:layout_weight="0"
        />
    <ProgressBar
        android:id="@android:id/progress"
        android:layout_width="match_parent"
        android:layout_height="8dp"
        android:visibility="gone"
        android:layout_weight="0"
        style="@style/Widget.Material.Light.ProgressBar.Horizontal"
        />
</merge>