Implement ObjectReference.ReferringObjects.

Bug: 4159882
Change-Id: Iac145715bec80b5900256d3f6bdb18e283eb9a12
diff --git a/src/debugger.h b/src/debugger.h
index ebcff08..c03adea 100644
--- a/src/debugger.h
+++ b/src/debugger.h
@@ -192,6 +192,9 @@
   static JDWP::JdwpError GetInstances(JDWP::RefTypeId class_id, int32_t max_count,
                                       std::vector<JDWP::ObjectId>& instances)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+  static JDWP::JdwpError GetReferringObjects(JDWP::ObjectId object_id, int32_t max_count,
+                                             std::vector<JDWP::ObjectId>& referring_objects)
+      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   /*
    * Method and Field