Prevent tabs sync during browser shutdown.

components/sync_sessions/sessions_sync_manager.cc

Index: components/sync_sessions/sessions_sync_manager.cc
diff --git a/components/sync_sessions/sessions_sync_manager.cc b/components/sync_sessions/sessions_sync_manager.cc
index d61d75591b9a75f8bf94956cfdbe0bec00c1797b..2c49b4b7dcd85020fb3d7f5f54352b327de39933 100644
--- a/components/sync_sessions/sessions_sync_manager.cc
+++ b/components/sync_sessions/sessions_sync_manager.cc
@@ -128,6 +128,7 @@ SessionsSyncManager::SessionsSyncManager(
                      sessions_client->GetHistoryService(),
                      kMaxSyncFavicons),
       local_tab_pool_out_of_sync_(true),
+      all_browsers_closing_(false),
       sync_prefs_(sync_prefs),
       local_device_(local_device),
       current_device_type_(sync_pb::SyncEnums_DeviceType_TYPE_OTHER),
@@ -469,6 +470,11 @@ void SessionsSyncManager::OnLocalTabModified(SyncedTabDelegate* modified_tab) {
     return;
   }
 
+  if (all_browsers_closing_) {
+    // Do not sync tabs closing during browser shutdown.
+    return;
+  }
+
   syncer::SyncChangeList changes;
   AssociateTab(modified_tab, &changes);
   // Note, we always associate windows because it's possible a tab became
@@ -485,6 +491,14 @@ void SessionsSyncManager::OnFaviconsChanged(const std::set<GURL>& page_urls,
     favicon_cache_.OnPageFaviconUpdated(page_url);
 }
 
+void SessionsSyncManager::SetAllBrowsersClosing(bool browsers_closing) {
+  all_browsers_closing_ = browsers_closing;
+}
+
+bool SessionsSyncManager::GetAllBrowsersClosingForTesting() {
+  return all_browsers_closing_;
+}
+
 void SessionsSyncManager::StopSyncing(syncer::ModelType type) {
   local_event_router_->Stop();
   if (sync_processor_.get() && lost_navigations_recorder_.get()) {