[SO-a/53453766/5690248] Android layout with horizontally expandable Constraints

expand_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<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:id="@+id/rootView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <android.support.constraint.ConstraintLayout
        android:id="@+id/target"
        android:layout_width="0dp"
        android:layout_height="200dp"
        android:background="#FF0000"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="@+id/right_view"
        app:layout_constraintStart_toStartOf="@+id/left_view"
        app:layout_constraintTop_toTopOf="parent">

        <TextView
            android:id="@+id/textView2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="8dp"
            android:gravity="center"
            android:text="Hello"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

    </android.support.constraint.ConstraintLayout>

    <TextView
        android:id="@+id/left_view"
        android:layout_width="1px"
        android:layout_height="wrap_content"
        android:singleLine="true"
        android:text="LEFT VIEW"
        app:layout_constraintEnd_toStartOf="@+id/left_guideline"
        app:layout_constraintTop_toTopOf="@+id/target"
        app:layout_constrainedWidth="true" />

    <TextView
        android:id="@+id/right_view"
        android:layout_width="1px"
        android:layout_height="wrap_content"
        android:text="RIGHT VIEW"
        app:layout_constraintStart_toStartOf="@+id/right_guideline"
        app:layout_constraintTop_toTopOf="@+id/target"
        app:layout_constrainedWidth="true"/>

    <Button
        android:id="@+id/left_btn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:layout_marginBottom="8dp"
        android:text="LEFT"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/right_btn"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/target" />

    <Button
        android:id="@+id/right_btn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:layout_marginBottom="8dp"
        android:text="RIGHT"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toEndOf="@+id/left_btn"
        app:layout_constraintTop_toBottomOf="@+id/target" />

    <android.support.constraint.Guideline
        android:id="@+id/left_guideline"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintGuide_percent="0.32" />

    <android.support.constraint.Guideline
        android:id="@+id/right_guideline"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintGuide_percent="0.68" />

</android.support.constraint.ConstraintLayout>