packages/SystemUI/res/layout/bubble_expanded_view.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  ~ Copyright (C) 2018 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
  -->
<com.android.systemui.bubbles.BubbleExpandedViewContainer
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="wrap_content"
    android:layout_width="match_parent"
    android:id="@+id/bubble_expanded_view">

    <View
        android:id="@+id/pointer_view"
        android:layout_width="@dimen/bubble_pointer_width"
        android:layout_height="@dimen/bubble_pointer_height"
    />

    <TextView
        android:id="@+id/bubble_content_header"
        android:background="@drawable/bubble_expanded_header_bg"
        android:textAppearance="@*android:style/TextAppearance.Material.Title"
        android:textSize="18sp"
        android:layout_width="match_parent"
        android:layout_height="@dimen/bubble_expanded_header_height"
        android:gravity="start|center_vertical"
        android:singleLine="true"
        android:paddingLeft="@dimen/bubble_expanded_header_horizontal_padding"
        android:paddingRight="@dimen/bubble_expanded_header_horizontal_padding"
    />

</com.android.systemui.bubbles.BubbleExpandedViewContainer>