Implement ReferenceType.Instances.

Change-Id: I6a72fc4c748e7041fedcb615eca2b86b1f28bb63
diff --git a/src/debugger.h b/src/debugger.h
index 1bad6cc..ebcff08 100644
--- a/src/debugger.h
+++ b/src/debugger.h
@@ -189,6 +189,9 @@
   static JDWP::JdwpError GetInstanceCounts(const std::vector<JDWP::RefTypeId>& class_ids,
                                            std::vector<uint64_t>& counts)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+  static JDWP::JdwpError GetInstances(JDWP::RefTypeId class_id, int32_t max_count,
+                                      std::vector<JDWP::ObjectId>& instances)
+      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   /*
    * Method and Field