ART: Add diagnostic for b/117426281

Print the type of the already-visited object.

Bug: 117426281
Test: art/test.py
Change-Id: I3b82b567788e835d35ac0cd3d2718fa58eefaf55
diff --git a/runtime/hprof/hprof.cc b/runtime/hprof/hprof.cc
index 9467c4c..f696e25 100644
--- a/runtime/hprof/hprof.cc
+++ b/runtime/hprof/hprof.cc
@@ -1073,7 +1073,8 @@
   if (obj->IsClass() && obj->AsClass()->IsRetired()) {
     return;
   }
-  DCHECK(visited_objects_.insert(obj).second) << "Already visited " << obj;
+  DCHECK(visited_objects_.insert(obj).second)
+      << "Already visited " << obj << "(" << obj->PrettyTypeOf() << ")";
 
   ++total_objects_;