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);

[Cutch, 2016/05/24 14:34:40]

Could we use stable ids for objects in the object store?

[rmacnak, 2016/05/24 16:31:38]

Not all of them. Many of the cache fields of the object store are reassigned
when the cache grows. The immutable fields are mostly known classes or libraries
that already have stable ids, so it don't think it is worth curating a list of
immutable fields in the object store and checking every object to see if it is
in one of those slots before giving it a ring id.

+    thread->isolate()->object_store()->PrintToJSONObject(&jsobj, false);
+    return true;
+  }
+
   PrintInvalidParamError(js, "objectId");
   return true;
 }