[nomaster] bring back SerializeStart from fa3b804

This is necessary to maintain binary compatibility with 2.10.0.

Author: adriaanm

bincompat-backward.whitelist.conf

@@ -11,16 +11,16 @@ filter {
             matchName="scala.collection.immutable.Stream.scala$collection$immutable$Stream$$loop$5"
             problemName=MissingMethodProblem
         },
-        {
-            # private[scala]
-            matchName="scala.collection.immutable.ListSerializeStart$"
-            problemName=MissingClassProblem
-        },
-        {
-            # private[scala]
-            matchName="scala.collection.immutable.ListSerializeStart"
-            problemName=MissingClassProblem
-        },
+        # {
+        #     # private[scala]
+        #     matchName="scala.collection.immutable.ListSerializeStart$"
+        #     problemName=MissingClassProblem
+        # },
+        # {
+        #     # private[scala]
+        #     matchName="scala.collection.immutable.ListSerializeStart"
+        #     problemName=MissingClassProblem
+        # },
         {
             # private nested class became private top-level class to fix SI-7018
             matchName="scala.reflect.macros.Attachments$NonemptyAttachments"

src/library/scala/collection/immutable/List.scala

@@ -642,6 +642,10 @@ object List extends SeqFactory[List] {
   }
 }
 
+/** Only used for list serialization */
+@SerialVersionUID(0L - 8287891243975527522L)
+private[scala] case object ListSerializeStart
+
 /** Only used for list serialization */
 @SerialVersionUID(0L - 8476791151975527571L)
 private[scala] case object ListSerializeEnd