res/layout/actionbar.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <TextView
        android:id="@+id/activity_title"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_alignParentLeft="true"
        android:layout_centerVertical="true"
        android:gravity="center"
        android:maxWidth="200dp"
        android:singleLine="true"
        android:textSize="20sp" />

    <Spinner
        android:id="@+id/account_selection"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_toRightOf="@+id/activity_title"
        android:layout_alignParentRight="true" />

</RelativeLayout>