session-android/res/layout/media_overview_gallery_item.xml

<?xml version="1.0" encoding="utf-8"?>
<org.thoughtcrime.securesms.components.SquareFrameLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:padding="2dp">

    <org.thoughtcrime.securesms.components.ThumbnailView
            android:id="@+id/image"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:contentDescription="@string/media_preview_activity__media_content_description" />

</org.thoughtcrime.securesms.components.SquareFrameLayout>