Abort sync cycles when download step fails

sync/engine/syncer.cc

Index: sync/engine/syncer.cc
diff --git a/sync/engine/syncer.cc b/sync/engine/syncer.cc
index 62c7af893ff2d6dc91d74c53980c7a50f4eef564..8cf93e0d0764637e4bfe1d645818fa3f5829c1dd 100644
--- a/sync/engine/syncer.cc
+++ b/sync/engine/syncer.cc
@@ -166,13 +166,19 @@ void Syncer::SyncShare(sessions::SyncSession* session,
       case STORE_TIMESTAMPS: {
         StoreTimestampsCommand store_timestamps;
         store_timestamps.Execute(session);
-        // We should download all of the updates before attempting to process
-        // them.
-        if (session->status_controller().ServerSaysNothingMoreToDownload() ||
-            !session->status_controller().download_updates_succeeded()) {
-          next_step = APPLY_UPDATES;
-        } else {
+        // We download all of the updates before attempting to apply them.
+        if (!session->status_controller().download_updates_succeeded()) {
+          // We may have downloaded some updates, but if the latest download
+          // attempt failed then we don't have all the updates.  We'll leave
+          // it to a retry job to pick up where we left off.
+          last_step = SYNCER_END; // Necessary for CONFIGURATION mode.
+          next_step = SYNCER_END;
+          DVLOG(1) << "Aborting sync cycle due to download updates failure";
+        } else if (!session->status_controller()
+                       .ServerSaysNothingMoreToDownload()) {
           next_step = DOWNLOAD_UPDATES;
+        } else {
+          next_step = APPLY_UPDATES;
         }
         break;
       }