CoordinatorLayout中的工具栏在Android 4.4中不可见（在Android 5.0中可见）

Question

这是一个带有工具栏，webView和浮动actionButton的布局（android 5.0中应该有一个浮动操作按钮）：

我使用了CoordinatorLayout，因为其中有一个浮动操作按钮。如果将其更改为LinearLayout，则操作栏将可见，但FloatingActionButton不会浮动在屏幕上。将CoordinatorLayout更改为FrameLayout不会进行任何更改。怎么处理这个？

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 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.support.design.widget.AppBarLayout
        android:id="@+id/appbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay">
        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar_custom"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:popupTheme="@style/AppTheme.PopupOverlay" />
    </android.support.design.widget.AppBarLayout>

        <WebView
            android:id="@+id/webView"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:scrollbarStyle="outsideOverlay" />

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab_favorite"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="end|bottom"
        android:layout_margin="@dimen/fab_margin"
        android:src="@drawable/ic_favorite_white_24dp"
        app:layout_behavior="com.drunkpiano.zhihuselection.utilities.ScrollingFavoriteFABBehavior" />


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

清单：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.drunkpiano.zhihuselection">

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity
            android:name=".activities.MainActivity"
            android:label="@string/app_name"
            android:theme="@style/AppTheme.NoActionBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".activities.WebViewActivity"
            android:label="@string/app_name"
            android:theme="@style/AppTheme.NoActionBar" />
        <activity android:name=".activities.FavoritesActivity" />
        <activity android:name=".activities.GuideActivity" />
        <activity android:name=".activities.AnyActivity"></activity>
    </application>

</manifest>

Styles.xml

<resources>

    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
        <!--<item name="android:listDivider">@drawable/shape_divider</item>-->
    </style>
    <style name="AppTheme.NoActionBar">
        <item name="windowActionBar">false</item>
        <item name="windowNoTitle">true</item>
    </style>
    <style name="AppTheme.AppBarOverlay" parent="ThemeOverlay.AppCompat.Dark.ActionBar" />
    <style name="AppTheme.PopupOverlay" parent="ThemeOverlay.AppCompat.Light" />


    <style name="ListItemText" parent="android:Widget.Holo.Light.TextView">
        <item name="android:gravity">center</item>
        <item name="android:layout_margin">5dip</item>
        <item name="android:minLines">3</item>
        <item name="android:textSize">14sp</item>
        <item name="android:textStyle">bold</item>
    </style>

    <style name="ThemeOverlay.YourApp" parent="ThemeOverlay.AppCompat.Dark.ActionBar" />
    <style name="ActionBarTheme" parent="Theme.AppCompat.Light.DarkActionBar" >
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
    </style>

</resources>