Limit visibility of sublists, make them implement RandomAccess

libraries/stdlib/src/kotlin/collections/AbstractList.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2016 JetBrains s.r.o.
+ * Copyright 2010-2017 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -44,7 +44,7 @@ public abstract class AbstractList<out E> protected constructor() : AbstractColl
 
     override fun subList(fromIndex: Int, toIndex: Int): List<E> = SubList(this, fromIndex, toIndex)
 
-    internal open class SubList<out E>(private val list: AbstractList<E>, private val fromIndex: Int, toIndex: Int) : AbstractList<E>() {
+    private class SubList<out E>(private val list: AbstractList<E>, private val fromIndex: Int, toIndex: Int) : AbstractList<E>(), RandomAccess {
         private var _size: Int = 0
 
         init {