Run change hooks and ref-updated events after indexing is done.

The change hooks and ref-updated events were run parallel to the
change (re)indexing. This meant that an event-stream sent events
to the clients before the change indexing was finished. If a client
queried for that change immediately after receiving the event it
happened that the response was not-found as the indexing wasn't yet
done.

Although we haven't had issues with a ref-updated event processors,
firing this event will also wait for the indexing task to finish
as we never know if a ref-updated event processor may trigger a
change query.

Change-Id: Iff17c5aeb9675f3991f938d31ef5048ef5b3b956

gerrit-server/src/main/java/com/google/gerrit/server/git/MergeOp.java

@@ -840,6 +840,7 @@ public class MergeOp {
       db.commit();
 
       sendMergedEmail(c, submitter);
+      indexer.index(db, c);
       if (submitter != null) {
         try {
           hooks.doChangeMergedHook(c,
@@ -852,7 +853,6 @@ public class MergeOp {
     } finally {
       db.rollback();
     }
-    indexer.index(db, c);
   }
 
   private Change setMergedPatchSet(Change.Id changeId, final PatchSet.Id merged)
@@ -1065,6 +1065,14 @@ public class MergeOp {
       }
     }));
 
+    if (indexFuture != null) {
+      try {
+        indexFuture.checkedGet();
+      } catch (IOException e) {
+        log.error("Failed to index new change message", e);
+      }
+    }
+
     if (submitter != null) {
       try {
         hooks.doMergeFailedHook(c,
@@ -1074,13 +1082,6 @@ public class MergeOp {
         log.error("Cannot run hook for merge failed " + c.getId(), ex);
       }
     }
-    if (indexFuture != null) {
-      try {
-        indexFuture.checkedGet();
-      } catch (IOException e) {
-        log.error("Failed to index new change message", e);
-      }
-    }
   }
 
   private void abandonAllOpenChanges() {