core: make SizeCounter use pointer instead of reference

Restore virtual inheritance of GenericLinkServiceCounters in
GenericLinkService

refs #3941

Change-Id: I368e4694fee7bc97173fddfc81d0c679da0d6eed
diff --git a/tests/core/counter.t.cpp b/tests/core/counter.t.cpp
index 310e589..ce9a086 100644
--- a/tests/core/counter.t.cpp
+++ b/tests/core/counter.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /**
- * Copyright (c) 2014-2015,  Regents of the University of California,
+ * Copyright (c) 2014-2017,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -69,16 +69,22 @@
 BOOST_AUTO_TEST_CASE(SizeCnt)
 {
   std::vector<int> v;
-  SizeCounter<std::vector<int>> counter(v);
+  SizeCounter<std::vector<int>> counter1(&v);
+  SizeCounter<std::vector<int>> counter2;
+  counter2.observe(&v);
 
-  size_t observation = counter; // implicit conversion
-  BOOST_CHECK_EQUAL(observation, 0);
+  size_t observation1 = counter1; // implicit conversion
+  size_t observation2 = counter2;
+  BOOST_CHECK_EQUAL(observation1, 0);
+  BOOST_CHECK_EQUAL(observation2, 0);
 
   v.resize(249);
-  BOOST_CHECK_EQUAL(counter, 249);
+  BOOST_CHECK_EQUAL(counter1, 249);
+  BOOST_CHECK_EQUAL(counter2, 249);
 
   v.resize(98);
-  BOOST_CHECK_EQUAL(counter, 98);
+  BOOST_CHECK_EQUAL(counter1, 98);
+  BOOST_CHECK_EQUAL(counter2, 98);
 }
 
 BOOST_AUTO_TEST_SUITE_END() // TestCounter