Include parent field/list index in retaining path.

runtime/vm/service.cc

Index: runtime/vm/service.cc
===================================================================
--- runtime/vm/service.cc	(revision 37797)
+++ runtime/vm/service.cc	(working copy)
@@ -981,19 +981,22 @@
       return true;
     }
     ObjectGraph graph(isolate);
-    Array& path = Array::Handle(Array::New(limit));
+    Array& path = Array::Handle(Array::New(limit * 2));
     intptr_t length = graph.RetainingPath(obj, path);
     JSONObject jsobj(js);
     jsobj.AddProperty("type", "RetainingPath");
     jsobj.AddProperty("id", "retaining_path");
     jsobj.AddProperty("length", length);
     JSONArray elements(&jsobj, "elements");
-    for (intptr_t i = 0; i < path.Length() && i < length; ++i) {
+    Object& element = Object::Handle();
+    Smi& offset_from_parent = Smi::Handle();
+    for (intptr_t i = 0; i < limit && i < length; ++i) {
       JSONObject jselement(&elements);
-      Object& element = Object::Handle();
-      element = path.At(i);
+      element = path.At(i * 2);
       jselement.AddProperty("index", i);
       jselement.AddProperty("value", element);
+      offset_from_parent ^= path.At((i * 2) + 1);
+      // TODO(koda): Interpret offset as field, list index or map entry.
     }
     return true;
   }