[Sync] Restore previous session if no tabbed windows present

ios/chrome/browser/sync/ios_chrome_synced_tab_delegate.mm

 // Copyright 2015 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 "ios/chrome/browser/sync/ios_chrome_synced_tab_delegate.h"
 
 #include "base/memory/ref_counted.h"
 #include "components/sessions/ios/ios_serialized_navigation_builder.h"
 #include "components/sync_sessions/sync_sessions_client.h"
 #include "components/sync_sessions/synced_window_delegate.h"
 #include "components/sync_sessions/synced_window_delegates_getter.h"
+#include "components/sync_sessions/tab_node_pool.h"
 #include "ios/chrome/browser/sessions/ios_chrome_session_tab_helper.h"
 #include "ios/web/public/favicon_status.h"
 #include "ios/web/public/navigation_item.h"
 #import "ios/web/public/navigation_manager.h"
 #include "ios/web/public/web_state/web_state.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 using web::NavigationItem;
 
 DEFINE_WEB_STATE_USER_DATA_KEY(IOSChromeSyncedTabDelegate);
 
 namespace {
 
 // Helper to access the correct NavigationItem, accounting for pending entries.
 NavigationItem* GetPossiblyPendingItemAtIndex(web::WebState* web_state, int i) {
   int pending_index = web_state->GetNavigationManager()->GetPendingItemIndex();
   return (pending_index == i)
              ? web_state->GetNavigationManager()->GetPendingItem()
              : web_state->GetNavigationManager()->GetItemAtIndex(i);
 }
 
 }  // namespace
 
 IOSChromeSyncedTabDelegate::IOSChromeSyncedTabDelegate(web::WebState* web_state)
-    : web_state_(web_state), sync_session_id_(0) {}
+    : web_state_(web_state),
+      sync_session_id_(sync_sessions::TabNodePool::kInvalidTabNodeID) {}
 
 IOSChromeSyncedTabDelegate::~IOSChromeSyncedTabDelegate() {}
 
 SessionID::id_type IOSChromeSyncedTabDelegate::GetWindowId() const {
   return IOSChromeSessionTabHelper::FromWebState(web_state_)->window_id().id();
 }
 
 SessionID::id_type IOSChromeSyncedTabDelegate::GetSessionId() const {
   return IOSChromeSessionTabHelper::FromWebState(web_state_)->session_id().id();
 }
@@ skipping 83 matching lines @@
   for (int i = 0; i < entry_count; ++i) {
     const GURL& virtual_url = GetVirtualURLAtIndex(i);
     if (!virtual_url.is_valid())
       continue;
 
     if (sessions_client->ShouldSyncURL(virtual_url))
       return true;
   }
   return false;
 }