core/res/res/layout/notification_template_material_conversation.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  ~ Copyright (C) 2020 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.internal.widget.ConversationLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/status_bar_latest_event_content"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:clipChildren="false"
    android:tag="conversation"
    android:theme="@style/Theme.DeviceDefault.Notification"
    >

    <FrameLayout
        android:layout_width="@dimen/conversation_content_start"
        android:layout_height="wrap_content"
        android:gravity="start|top"
        android:clipChildren="false"
        android:clipToPadding="false"
        android:paddingTop="12dp"
    >

        <FrameLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="top|center_horizontal"
        >

            <!-- Big icon: 52x52, 12dp padding left + top, 16dp padding right -->
            <ImageView
                android:id="@+id/conversation_icon"
                android:layout_width="@dimen/conversation_avatar_size"
                android:layout_height="@dimen/conversation_avatar_size"
                android:scaleType="centerCrop"
                android:importantForAccessibility="no"
            />

            <ViewStub
                android:layout="@layout/conversation_face_pile_layout"
                android:layout_width="@dimen/conversation_avatar_size"
                android:layout_height="@dimen/conversation_avatar_size"
                android:id="@+id/conversation_face_pile"
                />

            <FrameLayout
                android:id="@+id/conversation_icon_badge"
                android:layout_width="20dp"
                android:layout_height="20dp"
                android:layout_marginLeft="@dimen/conversation_badge_side_margin"
                android:layout_marginTop="@dimen/conversation_badge_side_margin"
                android:background="@drawable/conversation_badge_background" >
                <!-- Badge: 20x20, 48dp padding left + top -->
                <com.android.internal.widget.CachingIconView
                    android:id="@+id/icon"
                    android:layout_width="@dimen/conversation_icon_size_badged"
                    android:layout_height="@dimen/conversation_icon_size_badged"
                    android:layout_gravity="center"
                />
            </FrameLayout>
        </FrameLayout>
    </FrameLayout>

    <!-- Wraps entire "expandable" notification -->
    <com.android.internal.widget.RemeasuringLinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="top"
        android:clipToPadding="false"
        android:clipChildren="false"
        android:orientation="vertical"
        >
        <!-- LinearLayout for Expand Button-->
        <com.android.internal.widget.RemeasuringLinearLayout
            android:id="@+id/expand_button_and_content_container"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:gravity="start|top"
            android:orientation="horizontal"
            android:clipChildren="false"
            android:clipToPadding="false">
            <!--TODO: move this into a separate layout and share logic with the header to bring back app opps etc-->
            <com.android.internal.widget.RemeasuringLinearLayout
                android:id="@+id/notification_action_list_margin_target"
                android:layout_width="0dp"
                android:orientation="vertical"
                android:layout_height="wrap_content"
                android:layout_weight="1">

                <!-- Header -->
                <LinearLayout
                    android:id="@+id/conversation_header"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:orientation="horizontal"
                    android:paddingTop="16dp"
                    android:paddingStart="@dimen/conversation_content_start"
                >
                    <TextView
                        android:id="@+id/conversation_text"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_marginEnd="@dimen/notification_header_separating_margin"
                        android:textAppearance="@style/TextAppearance.DeviceDefault.Notification.Title"
                        android:textSize="16sp"
                        android:singleLine="true"
                        />

                    <TextView
                        android:id="@+id/time_divider"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:textAppearance="?attr/notificationHeaderTextAppearance"
                        android:layout_marginStart="@dimen/notification_header_separating_margin"
                        android:layout_marginEnd="@dimen/notification_header_separating_margin"
                        android:text="@string/notification_header_divider_symbol"
                        android:layout_gravity="center"
                        android:paddingTop="1sp"
                        android:singleLine="true"
                        android:visibility="gone"
                    />

                    <DateTimeView
                        android:id="@+id/time"
                        android:textAppearance="@style/TextAppearance.Material.Notification.Time"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_gravity="center"
                        android:layout_marginStart="@dimen/notification_header_separating_margin"
                        android:paddingTop="1sp"
                        android:showRelative="true"
                        android:singleLine="true"
                        android:visibility="gone"
                    />

                    <ImageView
                        android:id="@+id/profile_badge"
                        android:layout_width="@dimen/notification_badge_size"
                        android:layout_height="@dimen/notification_badge_size"
                        android:layout_gravity="center"
                        android:layout_marginStart="4dp"
                        android:paddingTop="2dp"
                        android:scaleType="fitCenter"
                        android:visibility="gone"
                        android:contentDescription="@string/notification_work_profile_content_description"
                    />
                </LinearLayout>

                <!-- Messages -->
                <com.android.internal.widget.MessagingLinearLayout
                    android:id="@+id/notification_messaging"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_marginTop="2dp"
                    android:spacing="@dimen/notification_messaging_spacing"
                    android:clipToPadding="false"
                    android:clipChildren="false"
                    />
            </com.android.internal.widget.RemeasuringLinearLayout>
            <!-- Unread Count -->
            <!-- <TextView /> -->

            <!-- This is where the expand button will be placed when collapsed-->
        </com.android.internal.widget.RemeasuringLinearLayout>

        <include layout="@layout/notification_template_smart_reply_container"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="@dimen/notification_content_margin"
            android:layout_marginStart="@dimen/conversation_content_start"
            android:layout_marginEnd="@dimen/notification_content_margin_end" />
        <include layout="@layout/notification_material_action_list" />
    </com.android.internal.widget.RemeasuringLinearLayout>

    <!--This is dynamically placed between here and at the end of the layout-->
    <FrameLayout
        android:id="@+id/expand_button_container"
        android:layout_width="wrap_content"
        android:layout_height="@dimen/conversation_expand_button_expanded_size"
        android:layout_gravity="end|top"
        android:paddingStart="16dp"
        android:paddingEnd="@dimen/notification_content_margin_end">
        <com.android.internal.widget.NotificationExpandButton
            android:id="@+id/expand_button"
            android:layout_width="@dimen/notification_header_expand_icon_size"
            android:layout_height="@dimen/notification_header_expand_icon_size"
            android:layout_gravity="center"
            android:drawable="@drawable/ic_expand_notification"
            android:clickable="false"
            android:importantForAccessibility="no"
            />
    </FrameLayout>
</com.android.internal.widget.ConversationLayout>