Signal-Android/res/layout/view_once_message_activity.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/core_black">

    <ImageView
        android:id="@+id/view_once_image"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scaleType="fitCenter"/>

    <ImageView
        android:id="@+id/view_once_close_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="19dp"
        android:layout_marginStart="19dp"
        android:tint="@color/core_white"
        app:srcCompat="@drawable/ic_x"/>

</FrameLayout>