Make the object store visible in Observatory.

runtime/vm/service.cc

Index: runtime/vm/service.cc
diff --git a/runtime/vm/service.cc b/runtime/vm/service.cc
index fc78a4879bb26214aa9c91ff5025ea6899a97b91..f3b8553468ab5df2171b275c6112d3e49698d408 100644
--- a/runtime/vm/service.cc
+++ b/runtime/vm/service.cc
@@ -3592,6 +3592,12 @@ static bool GetObject(Thread* thread, JSONStream* js) {
     return true;
   }
 
+  if (strcmp(id, "object_store") == 0) {
+    JSONObject jsobj(js);
+    thread->isolate()->object_store()->PrintToJSONObject(&jsobj, false);
+    return true;
+  }
+
   PrintInvalidParamError(js, "objectId");
   return true;
 }