title: ConstraintLayout layout_constraintHorizontal_bias seems not work
body: <p>This is my layout file.</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"
      xmlns:tools="http://schemas.android.com/tools"
      android:layout_width="match_parent"
      android:layout_height="match_parent"&gt;
      &lt;EditText
          android:layout_width="150dp"
          android:layout_height="50dp"
          android:hint="please input test content"
          android:inputType="phone"
          android:textColorHint="@android:color/holo_red_light"
          android:textSize="13sp"
          app:layout_constraintBottom_toTopOf="parent"
          app:layout_constraintRight_toLeftOf="parent" /&gt;
      &lt;TextView
          android:layout_width="80dp"
          android:layout_height="50dp"
          android:gravity="center"
          android:text="Hello"
          android:textColor="@android:color/black"
          app:layout_constraintBottom_toTopOf="parent"
          app:layout_constraintHorizontal_bias="0.5" /&gt;
  &lt;/android.support.constraint.ConstraintLayout&gt;
  </code></pre>
  
  <p>Follow pic is preview view.</p>
  
  <p><a href="https://i.stack.imgur.com/1Ctoa.png" rel="noreferrer"><img src="https://i.stack.imgur.com/1Ctoa.png" alt="enter image description here"></a></p>
  
  <p>I want to move TextView to center_horizontal to parent view , but <code>layout_constraintHorizontal_bias=0.5"</code> seems not work.</p>
  
  <p>Who has ideas for this problem ? Thanks for first !</p>