Using HeapSnapshotClassOutbound for outbound references

runtime/observatory/lib/src/heap_snapshot/heap_snapshot.dart

Index: runtime/observatory/lib/src/heap_snapshot/heap_snapshot.dart
diff --git a/runtime/observatory/lib/src/heap_snapshot/heap_snapshot.dart b/runtime/observatory/lib/src/heap_snapshot/heap_snapshot.dart
index d20fc0a182285d2c0fb8646dbba0efbe5db4c572..06241f981b3219262ef5fb2419cad3425668b104 100644
--- a/runtime/observatory/lib/src/heap_snapshot/heap_snapshot.dart
+++ b/runtime/observatory/lib/src/heap_snapshot/heap_snapshot.dart
@@ -196,7 +196,7 @@ class MergedVertex implements M.HeapSnapshotClassReferences {
       // https://github.com/dart-lang/sdk/issues/27144
       return _outbounds = new List<HeapSnapshotClassOutbound>.unmodifiable(
         outgoingEdges.values.map((edge) {
-          return new HeapSnapshotClassInbound(this, edge);
+          return new HeapSnapshotClassOutbound(this, edge);
         })
       );
     }