Removed dead code from NavigationManagerImpl::GetIndexForOffset.

ios/web/navigation/navigation_manager_impl.mm

Index: ios/web/navigation/navigation_manager_impl.mm
diff --git a/ios/web/navigation/navigation_manager_impl.mm b/ios/web/navigation/navigation_manager_impl.mm
index a059c1d0e3c19f4421442ccc06de66ddcc44dd38..863ba8a95395b861af114cf48b2e3194c08669b7 100644
--- a/ios/web/navigation/navigation_manager_impl.mm
+++ b/ios/web/navigation/navigation_manager_impl.mm
@@ -393,16 +393,6 @@ int NavigationManagerImpl::GetIndexForOffset(int offset) const {
     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;