WordPress/src/main/res/layout/reader_activity_post_pager.xml

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/root_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <org.wordpress.android.widgets.WPViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <include
        android:id="@+id/toolbar"
        layout="@layout/toolbar" />

    <ProgressBar
        android:id="@+id/progress_loading"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:visibility="gone"
        tools:visibility="visible" />

</RelativeLayout>