packages/DocumentsUI/res/layout/fixed_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright (C) 2013 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.
-->

<!-- CoordinatorLayout is necessary for various components (e.g. Snackbars, and
     floating action buttons) to operate correctly. -->
<!-- focusableInTouchMode is set in order to force key events to go to the activity's global key
     callback, which is necessary for proper event routing. See BaseActivity.onKeyDown. -->
<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/coordinator_layout"
    android:focusableInTouchMode="true">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <com.android.documentsui.DocumentsToolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?android:attr/actionBarSize"
            android:background="?android:attr/colorPrimary"
            android:elevation="8dp"
            android:theme="?actionBarTheme"
            android:popupTheme="?actionBarPopupTheme">

            <Spinner
                android:id="@+id/stack"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginStart="4dp"
                android:popupTheme="?actionBarPopupTheme"
                android:background="@android:color/transparent"
                android:overlapAnchor="true" />

        </com.android.documentsui.DocumentsToolbar>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="1"
            android:orientation="horizontal"
            android:baselineAligned="false">

            <FrameLayout
                android:id="@+id/container_roots"
                android:layout_width="256dp"
                android:layout_height="match_parent" />

            <include layout="@layout/directory_cluster"
                android:layout_width="0dp"
                android:elevation="8dp" />

        </LinearLayout>

    </LinearLayout>

</android.support.design.widget.CoordinatorLayout>