title: AppBarLayout elevation hides toolbar
body: <p>I'm trying to <a href="http://i.imgur.com/Z7loYl2.jpg" rel="noreferrer">disable the shadow below a transparent AppBarLayout/Toolbar.</a> Here's the layout:</p>
  
  <pre><code>&lt;android.support.design.widget.CoordinatorLayout
      xmlns:android="http://schemas.android.com/apk/res/android"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      android:background="#000"&gt;
  
      &lt;android.support.design.widget.AppBarLayout
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:fitsSystemWindows="true"
          android:background="@android:color/transparent"
          android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"&gt;
  
          &lt;android.support.v7.widget.Toolbar
              android:id="@+id/imagePreviewToolbar"
              android:layout_width="match_parent"
              android:layout_height="?attr/actionBarSize" /&gt;
  
      &lt;/android.support.design.widget.AppBarLayout&gt;
  
      &lt;include layout="@layout/content_image_preview" /&gt;
  &lt;/android.support.design.widget.CoordinatorLayout&gt;
  </code></pre>
  
  <p>I already tried with</p>
  
  <pre><code>app:elevation="0dp"
  </code></pre>
  
  <p>and</p>
  
  <pre><code>getSupportActionBar().setElevation(0);
  </code></pre>
  
  <p>but that makes <a href="http://i.imgur.com/t4sP1zh.jpg" rel="noreferrer">the UP arrow invisible</a>. I also tried to remove the AppBarLayout and use only the Toolbar, but the problem persists.</p>
  
  <p>Anyone has a solution?</p>
  
  <hr>
  
  <p><strong>EDIT:</strong></p>
  
  <p>Replacing the AppBarLayout + Toolbar combo with this code:</p>
  
  <pre><code>&lt;android.support.v7.widget.Toolbar
      android:id="@+id/imagePreviewToolbar"
      android:layout_width="match_parent"
      android:layout_height="?attr/actionBarSize"
      android:background="@android:color/transparent"
      android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
      app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
      app:elevation="0dp"/&gt;
  </code></pre>
  
  <p><em>partially</em> fixed the problem. Now the Toolbar becomes invisible only when the device is in landscape mode! The Android Studio Layout Editor shows me the Toolbar in both orientations just fine, so I don't really know what the problem could be..</p>