Merge pull request scala#4647 from Ichoran/issue/8911

SI-8911  allow serializing Scala Maps wrapped as Java ones

Author: lrytz

src/library/scala/collection/convert/Wrappers.scala

@@ -102,9 +102,9 @@ private[collection] trait Wrappers {
     override def clone(): JListWrapper[A] = JListWrapper(new ju.ArrayList[A](underlying))
   }
 
-  // Note various overrides to avoid performance gotchas.
-  class SetWrapper[A](underlying: Set[A]) extends ju.AbstractSet[A] {
-    self =>
+  @SerialVersionUID(1L)
+  class SetWrapper[A](underlying: Set[A]) extends ju.AbstractSet[A] with Serializable { self =>
+    // Note various overrides to avoid performance gotchas.
     override def contains(o: Object): Boolean = {
       try { underlying.contains(o.asInstanceOf[A]) }
       catch { case cce: ClassCastException => false }
@@ -165,7 +165,8 @@ private[collection] trait Wrappers {
       new JSetWrapper[A](new ju.LinkedHashSet[A](underlying))
   }
 
-  class MapWrapper[A, B](underlying: Map[A, B]) extends ju.AbstractMap[A, B] { self =>
+  @SerialVersionUID(1L)
+  class MapWrapper[A, B](underlying: Map[A, B]) extends ju.AbstractMap[A, B] with Serializable { self =>
     override def size = underlying.size
 
     override def get(key: AnyRef): B = try {