Prevent tabs sync during browser shutdown.

components/sync_sessions/local_session_event_router.h

Index: components/sync_sessions/local_session_event_router.h
diff --git a/components/sync_sessions/local_session_event_router.h b/components/sync_sessions/local_session_event_router.h
index 51b07c3db0317478256a4042a4da75ed571f89cf..4c1e0f609bfdcd24a82c204f3e47cc5250a63137 100644
--- a/components/sync_sessions/local_session_event_router.h
+++ b/components/sync_sessions/local_session_event_router.h
@@ -35,6 +35,11 @@ class LocalSessionEventHandler {
   virtual void OnFaviconsChanged(const std::set<GURL>& page_urls,
                                  const GURL& icon_url) = 0;
 
+  // A flag set when browsers are closing, so we shouldn't send tabs
+  // closing events to sync server. Tabs will be restored on the next browser
+  // start.
+  virtual void SetAllBrowsersClosing(bool browsers_closing) = 0;
+
  protected:
   LocalSessionEventHandler() {}