title: ConstraintLayout issue with horizontal weight
body: <p>Consider following xml layout:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;android.support.constraint.ConstraintLayout
      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"&gt;
  
      &lt;Button
          android:id="@+id/b1"
          android:layout_width="0dp"
          android:layout_height="wrap_content"
          android:text="B1"
          app:layout_constraintHorizontal_weight="1"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintRight_toLeftOf="@+id/b2"/&gt;
  
      &lt;Button
          android:id="@+id/b2"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:text="B2"
          app:layout_constraintLeft_toRightOf="@+id/b1"
          app:layout_constraintRight_toLeftOf="@id/b3"/&gt;
  
      &lt;Button
          android:id="@+id/b3"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:text="B3"
          app:layout_constraintLeft_toRightOf="@+id/b2"
          app:layout_constraintRight_toRightOf="parent"/&gt;
  &lt;/android.support.constraint.ConstraintLayout&gt;
  </code></pre>
  
  <p>which produces this layout which is what I want:</p>
  
  <p><a href="https://i.stack.imgur.com/Xj1sq.png" rel="noreferrer"><img src="https://i.stack.imgur.com/Xj1sq.png" alt="enter image description here"></a></p>
  
  <p>But if I mark B3 as gone then B1's width is set to 0 and B2 move to left. Whereas I want B2 to take B3's place and B1 to expand:</p>
  
  <p><a href="https://i.stack.imgur.com/6lKAU.png" rel="noreferrer"><img src="https://i.stack.imgur.com/6lKAU.png" alt="enter image description here"></a></p>
  
  <p>Any idea what I might be doing wrong?</p>