Fix TreeMap serialization tests.

These are fixed by adding an explicit serialVersionUID. Note
that the jdk8 version of this class in the RI isn't serialization
compatible with the jdk7 version of this class.

bug: 27426688
Change-Id: I9a0ad778b24503f196d35b7273bdd3ddf4ccb407
diff --git a/ojluni/src/main/java/java/util/TreeMap.java b/ojluni/src/main/java/java/util/TreeMap.java
index 7a67e01..76e9b00 100755
--- a/ojluni/src/main/java/java/util/TreeMap.java
+++ b/ojluni/src/main/java/java/util/TreeMap.java
@@ -1328,6 +1328,12 @@
      */
     abstract static class NavigableSubMap<K,V> extends AbstractMap<K,V>
         implements NavigableMap<K,V>, java.io.Serializable {
+        // Android-changed: Explicitly add a serialVersionUID so that we're serialization
+        // compatible with the Java-7 version of this class. Several new methods were added
+        // in Java-8 but none of them have any bearing on the serialized format of the class
+        // or require any additional state to be preserved.
+        private static final long serialVersionUID = 2765629423043303731L;
+
         /**
          * The backing map.
          */