title: Constraint Layout does'nt constraint nested elements of other layouts
body: <p>I'm trying to create a layout of a list which starts on the bottom of a button and it's 3/4 of screen's width. </p>
  
  <p>Just like this:</p>
  
  <p><a href="https://i.stack.imgur.com/mKqhu.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/mKqhu.png" alt="imagine that there is a button instead of a bar"></a></p>
  
  <p>First, I used nested Linear layouts a horizonal and a vertical one, but then I read <a href="https://developer.android.com/training/constraint-layout/" rel="nofollow noreferrer">here</a> that Constraint layouts are more responsive and I was impressed and gave it a try.</p>
  
  <p>So, I tried to replace the outer layout to a constraint layout but now, I can't constraint the list to start at the <strong>bottom</strong> of the button and it starts at top of the screen.
  I tried to see what would happen if I replaced the whole linear layout with a button just to see that the attributes are correctly implemented and it worked, so I understood that the Constraint layout does'nt effect the sons of the Linear layout although it should be effecting the whole layout (as I see it).</p>
  
  <p>my code is the following:</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"
      tools:context=".MainActivity"&gt;
  
  
      &lt;ImageButton
          android:id="@+id/settings_button"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:backgroundTint="#FFFFFF"
          android:src="@drawable/ic_menu_black_32dp"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintTop_toTopOf="parent"/&gt;
  
      &lt;LinearLayout
          android:id="@+id/list_linear_layout"
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:weightSum="4"
          app:layout_constraintBottom_toBottomOf="parent"
          app:layout_constraintStart_toStartOf="parent"
          app:layout_constraintEnd_toStartOf="@+id/settings_button"
          app:layout_constraintTop_toBottomOf="@+id/settings_button"&gt;
  
          &lt;ListView
              android:id="@+id/listview"
              android:layout_width="0dp"
              android:layout_height="match_parent"
              android:layout_weight="3" /&gt;
      &lt;/LinearLayout&gt;
  
  &lt;/android.support.constraint.ConstraintLayout&gt;
  </code></pre>
  
  <p><strong>My current layout looks like this:</strong></p>
  
  <p><a href="https://i.stack.imgur.com/oxkdZ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/oxkdZ.png" alt="current layout"></a></p>
  
  <p><strong><em>I really appriciate the helpers!</em></strong></p>