[geary/wip/713530-background-sync: 4/6] Add some debugging so we know when a background sync has completed.

[Michael Gratton <mjog src gnome org>]

commit 5ccc88fcafac7d0dbe596f3fce5284a2c124d628
Author: Michael James Gratton <mike vee net>
Date:   Fri Dec 1 13:19:48 2017 +1100

    Add some debugging so we know when a background sync has completed.

 .../imap-engine-account-synchronizer.vala          |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/src/engine/imap-engine/imap-engine-account-synchronizer.vala 
b/src/engine/imap-engine/imap-engine-account-synchronizer.vala
index 522313d..ca0101e 100644
--- a/src/engine/imap-engine/imap-engine-account-synchronizer.vala
+++ b/src/engine/imap-engine/imap-engine-account-synchronizer.vala
@@ -352,6 +352,10 @@ private class Geary.ImapEngine.AccountSynchronizer : Geary.BaseObject {
                 }
             }
         }
+        Logging.debug(
+            Logging.Flag.PERIODIC, "Background sync of %s completed",
+            folder.to_string()
+        );
     }
 
     private async void sync_folder_async(MinimalFolder folder,