packages/SystemUI/res/layout/notification_header.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  ~ Copyright (C) 2015 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.statusbar.notification.NotificationHeaderView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="@dimen/notification_header_height"
    android:clipChildren="false">
    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="wrap_content"
        android:layout_height="@dimen/notification_header_height"
        android:layout_gravity="start"
        android:gravity="center_vertical"
        android:paddingStart="@dimen/notification_content_margin_start">
        <ImageView
            android:id="@+id/header_notification_icon"
            android:layout_width="24dp"
            android:layout_height="24dp"
            android:layout_marginEnd="4dp"
            />
        <TextView
            android:id="@+id/number_of_children"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textAppearance="@*android:style/TextAppearance.Material.Notification"
            android:layout_marginEnd="2dp"
            android:layout_marginStart="1dp"
            />
        <TextView
            android:id="@+id/app_name_text"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textAppearance="@style/TextAppearance.Material.Notification.HeaderTitle"
            android:layout_marginStart="4dp"
            android:layout_marginEnd="8dp"
            />
        <TextView
            android:id="@+id/app_title_sub_text_divider"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textAppearance="@style/TextAppearance.Material.Notification.HeaderTitle"
            android:layout_marginEnd="8dp"
            android:text="@string/notification_header_divider_symbol"/>
        <TextView
            android:id="@+id/title_sub_text"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textAppearance="@style/TextAppearance.Material.Notification.HeaderTitle"
            android:layout_marginEnd="8dp" />
        <TextView
            android:id="@+id/post_time"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="end|center_vertical"
            android:textAppearance="@*android:style/TextAppearance.Material.Notification.Time"
            android:paddingEnd="8dp"
            />
    </LinearLayout>
    <ImageButton
        android:id="@+id/notification_expand_button"
        android:background="@null"
        android:layout_width="48dp"
        android:layout_height="48dp"
        android:layout_gravity="end|center_vertical"
        android:src="@drawable/notification_expand_more"
        android:layout_marginEnd="8dp"
        />
</com.android.systemui.statusbar.notification.NotificationHeaderView>