<android.support.constraint.Guideline
    android:id="@+id/guideline"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    app:layout_constraintGuide_percent="0.3" />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:layout_constraintTop_toTopOf="@id/guideline"
    app:layout_constraintBottom_toBottomOf="@id/guideline" />