message: Print both assigned and requested device in `Node::DebugString()`
  At the moment the requested device is not present in the debug output
diff: @@ -113,9 +113,9 @@ std::string Node::DebugString() const {
  } else if (IsSink()) {
  strings::StrAppend(&ret, " sink}");
  } else {
  - strings::StrAppend(&ret, " op device:");
  - strings::StrAppend(&ret, "{", assigned_device_name(), "}");
  - strings::StrAppend(&ret, " def:{", SummarizeNode(*this), "}}");
  + strings::StrAppend(&ret, " op device:", "{requested: '", requested_device(),
  + "', assigned: '", assigned_device_name(), "'}", " def:{",
  + SummarizeNode(*this), "}}");
  }
  return ret;
  }
  