Bookmark: Fix a legacy DCHECK in bookmark bridge.

Currently bookmark root node has 4 children instead of 5. The DCHECK
is never ran.

The java code calling into this is probably dead code, added a comment.

Bug: 1148498
Change-Id: I20630b20ba8454665a8d1721f62e2baa312263b0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2535923Reviewed-by: Theresa  <twellington@chromium.org>
Reviewed-by: Brandon Wylie <wylieb@chromium.org>
Commit-Queue: Xing Liu <xingliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827192}

chrome/browser/android/bookmarks/bookmark_bridge.cc

@@ -299,8 +299,7 @@ void BookmarkBridge::GetTopLevelFolderIDs(
   std::size_t special_count = top_level_folders.size();
 
   if (get_normal) {
-    DCHECK_EQ(5u, bookmark_model_->root_node()->children().size());
-
+    DCHECK_EQ(4u, bookmark_model_->root_node()->children().size());
     for (const auto& node : bookmark_model_->mobile_node()->children()) {
       if (node->is_folder())
         top_level_folders.push_back(node.get());