Removed dead code from NavigationManagerImpl::GetIndexForOffset.

ios/web/navigation/navigation_manager_impl.mm

 // Copyright 2013 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.
 
 #import "ios/web/navigation/navigation_manager_impl.h"
 
 #include <stddef.h>
 
 #include <utility>
 
@@ skipping 375 matching lines @@
       }
       --result;
       ++offset;
     }
     // Result may be out of bounds, so stop trying to skip redirect items and
     // simply add the remainder.
     result += offset;
     if (result > GetItemCount() /* overflow */)
       result = INT_MIN;
   } else if (offset > 0) {
-    if (GetPendingItem() && [session_controller_ pendingItemIndex] == -1) {
-      // Chrome for iOS does not allow forward navigation if there is another
-      // pending navigation in progress. Returning invalid index indicates that
-      // forward navigation will not be allowed (and |INT_MAX| works for that).
-      // This is different from other platforms which allow forward navigation
-      // if pending item exist.
-      // TODO(crbug.com/661858): Remove this once back-forward navigation uses
-      // pending index.
-      return INT_MAX;
-    }
     while (offset > 0 && result < GetItemCount()) {
       ++result;
       --offset;
       // As with going back, skip over redirects.
       while (result + 1 < GetItemCount() && IsRedirectItemAtIndex(result + 1)) {
         ++result;
       }
     }
     // Result may be out of bounds, so stop trying to skip redirect items and
     // simply add the remainder.
@@ skipping 33 matching lines @@
   const ScopedNavigationItemImplList& items = [session_controller_ items];
   while (index >= 0) {
     NavigationItem* item = items[index--].get();
     if (!client->IsAppSpecificURL(item->GetVirtualURL()))
       return item;
   }
   return nullptr;
 }
 
 }  // namespace web