Return empty array from GetBackwardItems and GetForwardItems during session restoration.

This will prevent showing Back And Forward items in the app UI.

Bug: 877671
Change-Id: I93f7868847a58e82d70fc01ebfb11a3a7d30399a
Reviewed-on: https://chromium-review.googlesource.com/c/1356982Reviewed-by: Danyao Wang <danyao@chromium.org>
Commit-Queue: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#613369}

ios/web/navigation/wk_based_navigation_manager_impl.mm

@@ -428,6 +428,9 @@ void WKBasedNavigationManagerImpl::GoForward() {
 NavigationItemList WKBasedNavigationManagerImpl::GetBackwardItems() const {
   NavigationItemList items;
 
+  if (is_restore_session_in_progress_)
+    return items;
+
   // If the current navigation item is a transient item (e.g. SSL
   // interstitial), the last committed item should also be considered part of
   // the backward history.
@@ -445,6 +448,10 @@ NavigationItemList WKBasedNavigationManagerImpl::GetBackwardItems() const {
 
 NavigationItemList WKBasedNavigationManagerImpl::GetForwardItems() const {
   NavigationItemList items;
+
+  if (is_restore_session_in_progress_)
+    return items;
+
   for (int index = web_view_cache_.GetCurrentItemIndex() + 1;
        index < GetItemCount(); index++) {
     items.push_back(GetItemAtIndex(index));

ios/web/web_state/web_state_unittest.mm

@@ -353,11 +353,11 @@ TEST_P(WebStateTest, RestoreLargeSession) {
                     navigation_manager->CanGoForward();
     if (!restored) {
       EXPECT_FALSE(navigation_manager->CanGoForward());
+      EXPECT_TRUE(navigation_manager->GetBackwardItems().empty());
+      EXPECT_TRUE(navigation_manager->GetForwardItems().empty());
       DCHECK_EQ(0.0, web_state_ptr->GetLoadingProgress());
       // TODO(crbug.com/877671): Ensure that the following API work correctly:
       //  - WebState::GetLastCommittedURL
-      //  - NavigationManager::GetBackwardItems
-      //  - NavigationManager::GetForwardItems
       //  - NavigationManager::GetLastCommittedItem
       //  - NavigationManager::GetPendingItem
       //  - NavigationManager::GetLastCommittedItemIndex