Add timing prints to object group to get a baseline.

runtime/observatory/lib/object_graph.dart

Index: runtime/observatory/lib/object_graph.dart
diff --git a/runtime/observatory/lib/object_graph.dart b/runtime/observatory/lib/object_graph.dart
index 60e720d3ac335b03181a376acfbd6369b4840625..0394d6d1d0474ab5660c3a16d15a1ab978b76f28 100644
--- a/runtime/observatory/lib/object_graph.dart
+++ b/runtime/observatory/lib/object_graph.dart
@@ -654,6 +654,8 @@ class ObjectGraph {
       }
     }
 
+    Logger.root.info("Start remap dominators");
+
     // Reindex doms by id instead of post order index so we can throw away
     // the post order arrays.
     var domById = new Uint32List(N + 1);
@@ -661,6 +663,8 @@ class ObjectGraph {
       domById[id] = postOrder[domByPOI[postOrderIndex[id]]];
     }
 
+    Logger.root.info("End remap dominators");
+
     domById[root] = 0;
 
     _doms = domById;