Avoid getSuperclass being native.

Add unit test from Change Iaf3e98ed

Change-Id: Ic408d2f781a5822506c31a270eb1e61ada929c53
diff --git a/src/jni_internal_test.cc b/src/jni_internal_test.cc
index fabd813..7db74a7 100644
--- a/src/jni_internal_test.cc
+++ b/src/jni_internal_test.cc
@@ -436,8 +436,11 @@
   ASSERT_TRUE(object_class != NULL);
   jclass string_class = env_->FindClass("java/lang/String");
   ASSERT_TRUE(string_class != NULL);
+  jclass runnable_interface = env_->FindClass("java/lang/Runnable");
+  ASSERT_TRUE(runnable_interface != NULL);
   ASSERT_TRUE(env_->IsSameObject(object_class, env_->GetSuperclass(string_class)));
   ASSERT_TRUE(env_->GetSuperclass(object_class) == NULL);
+  ASSERT_TRUE(env_->IsSameObject(object_class, env_->GetSuperclass(runnable_interface)));
 }
 
 TEST_F(JniInternalTest, IsAssignableFrom) {