title: Bottom of ScrollView clipped when using ConstraintLayout
body: <p>I have an issue using a <code>ScrollView</code> inside <code>ConstraintLayout</code> (<code>constraint-layout:1.0.0-beta3</code>)</p>
  
  <p>The content of my ScrollView isn't showed entirely.</p>
  
  <p>Here is my layout:</p>
  
  <pre><code>&lt;android.support.constraint.ConstraintLayout 
      xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      android:id="@+id/activity_test"
      android:layout_width="match_parent"
      android:layout_height="match_parent"&gt;
  
      &lt;LinearLayout
          android:id="@+id/header"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:orientation="horizontal"
          app:layout_constraintRight_toRightOf="parent"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintTop_toTopOf="parent"
          android:background="#212121"&gt;
  
          &lt;TextView
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:text="Constraint Layout"
              android:textSize="45sp"/&gt;
  
      &lt;/LinearLayout&gt;
  
      &lt;ScrollView
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          app:layout_constraintTop_toBottomOf="@+id/header"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintRight_toRightOf="parent"&gt;
  
          &lt;LinearLayout
              android:layout_width="match_parent"
              android:layout_height="wrap_content"
              android:orientation="vertical"&gt;
  
              &lt;Button
                  android:layout_width="match_parent"
                  android:layout_height="wrap_content"
                  android:text="BUTTON"
                  android:layout_marginTop="800dp"/&gt;
  
  
          &lt;/LinearLayout&gt;
  
      &lt;/ScrollView&gt;
  
  &lt;/android.support.constraint.ConstraintLayout&gt;
  </code></pre>
  
  <p>And here is the result</p>
  
  <p><a href="https://i.stack.imgur.com/ehXuj.png" rel="noreferrer"><img src="https://i.stack.imgur.com/ehXuj.png" alt="enter image description here"></a></p>
  
  <p>As you can see the button isn't visible and I reached the bottom of my ScrollView.</p>
  
  <p>It seems to works well with LinearLayout with layout below</p>
  
  <pre><code>&lt;LinearLayout 
      xmlns:android="http://schemas.android.com/apk/res/android"
      android:id="@+id/activity_test"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:orientation="vertical"&gt;
  
      &lt;LinearLayout
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:orientation="horizontal"
          android:background="#212121"&gt;
  
          &lt;TextView
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:text="Linear Layout"
              android:textSize="45sp"/&gt;
  
      &lt;/LinearLayout&gt;
  
      &lt;ScrollView
          android:layout_width="match_parent"
          android:layout_height="wrap_content"&gt;
  
          &lt;LinearLayout
              android:layout_width="match_parent"
              android:layout_height="wrap_content"
              android:orientation="vertical"&gt;
  
              &lt;Button
                  android:layout_width="match_parent"
                  android:layout_height="wrap_content"
                  android:text="BUTTON"
                  android:layout_marginTop="800dp"/&gt;
  
  
          &lt;/LinearLayout&gt;
  
      &lt;/ScrollView&gt;
  
  &lt;/LinearLayout&gt;
  </code></pre>
  
  <p>And result is</p>
  
  <p><a href="https://i.stack.imgur.com/FaggN.png" rel="noreferrer"><img src="https://i.stack.imgur.com/FaggN.png" alt="enter image description here"></a></p>
  
  <p>With LinearLayout end of ScrollView is reachable.</p>
  
  <p>Is there a bug with ConstraintLayout or do I made something wrong?</p>