Populate ChangeAttribute.createdOn by default

This allows for aggregating review-time if defined as the timespan
between when a change is created and when it is merged.
    event.eventCreatedOn - event.change.createdOn

This metric is valuable to get some sense of how effective your
code-review strategy/practice is, which in turn allows you to get a
sense for how effective actions to improve review-time is.

Change-Id: I7344ea07dad70bac871dcca0051164af20b80682
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/events/EventFactory.java b/gerrit-server/src/main/java/com/google/gerrit/server/events/EventFactory.java
index 80dcb78..5c6d06b 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/events/EventFactory.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/events/EventFactory.java
@@ -156,6 +156,7 @@
     a.owner = asAccountAttribute(change.getOwner());
     a.assignee = asAccountAttribute(change.getAssignee());
     a.status = change.getStatus();
+    a.createdOn = change.getCreatedOn().getTime() / 1000L;
     return a;
   }
 
@@ -185,7 +186,6 @@
    * @param change
    */
   public void extend(ChangeAttribute a, Change change) {
-    a.createdOn = change.getCreatedOn().getTime() / 1000L;
     a.lastUpdated = change.getLastUpdatedOn().getTime() / 1000L;
     a.open = change.getStatus().isOpen();
   }