[Sync] Fix flakiness from Sessions refactor

components/sync_sessions/sessions_sync_manager.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/sync_sessions/sessions_sync_manager.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/format_macros.h"
@@ skipping 349 matching lines @@
     return;
 
   SessionID::id_type tab_id = tab_delegate->GetSessionId();
   DVLOG(1) << "Syncing tab " << tab_id << " from window "
            << tab_delegate->GetWindowId();
 
   int tab_node_id = TabNodePool::kInvalidTabNodeID;
   bool existing_tab_node =
       session_tracker_.GetTabNodeForLocalTab(tab_id, &tab_node_id);
   DCHECK_NE(TabNodePool::kInvalidTabNodeID, tab_node_id);
+  tab_delegate->SetSyncId(tab_node_id);

[skym, 2016/12/09 15:40:00]

I can't seem to find anywhere that reads this value (that's not clearly
placeholder logic). But I suppose consistency isn't bad.

[Nicolas Zea, 2016/12/09 17:33:36]

Correct, we only use it for placeholders today (although perhaps in the future
that will expand)

   sessions::SessionTab* session_tab =
       session_tracker_.GetTab(current_machine_tag(), tab_id);
 
   // Get the previously synced url.
   int old_index = session_tab->normalized_navigation_index();
   GURL old_url;
   if (session_tab->navigations.size() > static_cast<size_t>(old_index))
     old_url = session_tab->navigations[old_index].virtual_url();
 
   // Update the tracker's session representation.
@@ skipping 379 matching lines @@
     // with tab_node_id changing from NodeIDB to NodeIDA.
     //
     // We can also wind up here if we created this tab as an out-of-order
     // update to the header node for this session before actually associating
     // the tab itself, so the tab node id wasn't available at the time and
     // is currently kInvalidTabNodeID.
     //
     // In both cases, we can safely throw it into the set of node ids.
     session_tracker_.OnTabNodeSeen(session_tag, specifics.tab_node_id());
     sessions::SessionTab* tab = session_tracker_.GetTab(session_tag, tab_id);
-    if (tab->timestamp > modification_time) {
+    if (!tab->timestamp.is_null() && tab->timestamp > modification_time) {
       DVLOG(1) << "Ignoring " << session_tag << "'s session tab " << tab_id
-               << " with earlier modification time";
+               << " with earlier modification time: " << tab->timestamp
+               << " vs " << modification_time;
       return;
     }
 
     // Update SessionTab based on protobuf.
     tab->SetFromSyncData(tab_s, modification_time);
 
     // If a favicon or favicon urls are present, load the URLs and visit
     // times into the in-memory favicon cache.
     RefreshFaviconVisitTimesFromForeignTab(tab_s, modification_time);
 
@@ skipping 334 matching lines @@
 }
 
 // static
 std::string SessionsSyncManager::TagHashFromSpecifics(
     const sync_pb::SessionSpecifics& specifics) {
   return syncer::GenerateSyncableHash(syncer::SESSIONS,
                                       TagFromSpecifics(specifics));
 }
 
 };  // namespace sync_sessions