The Attribute classes are moved from: com.google.gerrit.server.events to the newly created package: com.google.gerrit.server.data The `QueryStats` class is renamed to `QueryStatsAttribute` to be consistent with the other classes in the package. This is only a code reorganisation. No functionality is changed. Change-Id: I5c125e8d45d8f8e6943021cd90ddba1c364a103e