ui/base/models: Add empty() accessor to TreeNode class.

chrome/browser/importer/profile_writer.cc

Index: chrome/browser/importer/profile_writer.cc
diff --git a/chrome/browser/importer/profile_writer.cc b/chrome/browser/importer/profile_writer.cc
index da6397683ce8ef3c37c5c4d9e37892e019f254e5..fb194429a104a4111c8c154188e14fa454e68513 100644
--- a/chrome/browser/importer/profile_writer.cc
+++ b/chrome/browser/importer/profile_writer.cc
@@ -122,7 +122,7 @@ void ProfileWriter::AddBookmarks(const std::vector<BookmarkEntry>& bookmarks,
   // If the bookmark bar is currently empty, we should import directly to it.
   // Otherwise, we should import everything to a subfolder.
   const BookmarkNode* bookmark_bar = model->GetBookmarkBarNode();
-  bool import_to_top_level = bookmark_bar->child_count() == 0;
+  bool import_to_top_level = bookmark_bar->empty();
 
   // If the user currently has no bookmarks in the bookmark bar, make sure that
   // at least some of the imported bookmarks end up there.  Otherwise, we'll end